The Role of Consumers’ Individual Differences and Perceived Product Quality in Sustainable Luxury Marketing: An Experimental Study in a Social Media Context

Sustainability has become a central issue for luxury marketers and managers. By considering the luxury sector, consumers are more interested in buying sustainable products. However, luxury brands need to find the right way to communicate their sustainable products, especially in the online context. This paper sheds light on the differentiated effect of a luxury product communication message focused on an internalized versus externalized luxury approach in social media platforms context. Internalized luxury refers to luxury consumption mainly driven by individual style, while externalized luxury consumption refers to luxury consumption mainly driven by status. Results show that a sustainable luxury product communication focused on internalized (vs. externalized) luxury activates a greater perception of product quality, which in turn leads to a greater intention to buy. Theoretical contributions and implications for luxury brand managers are discussed.


Introduction
The boom in the luxury sector and its growing economic relevance has prompted scholars, academics, and managers to explore the concept of luxury, investigating the dimensions of luxury and identifying the drivers of luxury consumption (Atwal & Williams, 2017;Dubois et al., 2020). However, despite the interest of scholars in the study of luxury consumption, there is not a universal definition of luxury yet (Belk, 1999;Mundel et al., 2017). Pantano et al. (2018) sustained that luxury represents people leading an exclusive and inaccessible lifestyle dominated by wealth and consumption is driven by social attributes such as self-expression and the need to exhibit social standing. Furthermore, Nia and Lynne Zaichkowsky (2000), highlighted that luxury is a state of prestige and the possession of a luxury item is not associated with a functional utility. The construct of luxury is linked to different aspects such as sensual experiences and premium price (Kapferer, 1997), but not to production costs (Nueno & Quelch, 1998), and luxury product-related characteristics in terms of quality, uniqueness, and rarity (Roux;1991;Vigneron & Johnson, 2004). Although the concept of luxury still presents a certain non-univocity, the literature on the luxury brand has intended to outline specific characteristics associated with it (Ko et al., 2019;Maman Larraufie & Kourdoughli, 2014;Roux;1991;Sung et al., 2015;Vigneron & Johnson, 2004). In this context, the literature stresses that a single definition of luxury products must include six fundamental characteristics that is authenticity, quality, premium price, resonance, visibility and prestige (as in Godey et al., 2016;Colella et al., 2019). Hudders et al. (2013) pointed out that luxury brands are represented by a mix of characteristics such as exclusivity, uniqueness, scarcity, premium price, great quality and aesthetics. Importantly, by offering premium products, luxury brands tend to arouse pleasure for consumers at an emotional level (Hagtveded & Patrick, 2009). Moreover, from the literature it emerges that quality is a key characteristic of luxury brands (Keller, 2009;Ko et al., 2019;Okonkwo, 2007). The recent economic growth has coincided with a mounting commitment toward sustainable development among luxury brands (Kadam & Deshmukh, 2019). Despite the relevance of sustainability for luxury brands and consumers, research mainly investigated sustainable consumption in the context of mass-market products and brands (Lunde, 2018). In particular, to the best of the authors' knowledge, there is a lack of insights about what kind of communication-related to sustainable luxury products is more effective and what is the underlying process. Indeed, today, marketers and managers are increasingly committed to communicating sustainability with the aim of building and consolidating their image, trust, and reputation towards the brand and their products (Park & Kim, 2016). In this sense, the growing concern for environmental issues is urging companies to implement different marketing practices that focus primarily on sustainability (Kotler, 2011).
By considering the increased online presence of many brands today, pro-environmental initiatives aimed to lead sustainable consumption could be conveyed through digital tools reaching more effectiveness (Reilly & Weiru, 2012;Reilly & Hynan, 2014), also by leveraging on consumers' consumption for environmentally friendly products in the attempt to show other their "green" status (Griskevicius et al., 2010;. Among the wide range of digital tools, nowadays, social media may leverage on social interaction to create, distribute and support individuals' consumption though a deeper content creation strategies, to favour consumers' positive attitutes toward their products (Lee et al., 2018;Tsai & Men, 2013), e.g., by communicating their products as more sustainable rather the other (Reilly & Hynan, 2014), and exploiting online data to stimulate certain consumption behaviours (Sestino & De Mauro, 2021). Accordingly, Kaplan and Haenlein (2010, p. 61) define social media platforms as "a group of Internet-based applications that are based on the ideological and technological foundations of Web 2.0, enabling the creation and exchange of user-generated content". In this sense, social media play an important role in the implementation of global communication strategies of companies (Castronovo & Huang, 2012). According to Obar and Wildman (2015), user-generated content on social media platforms is the lifeblood of online communication, as it allows to connect and reach more people in their social communities and could thus be one of the main communication vehicles of content related to a luxury brand (Godey et al., 2016). Thus, we would shed light on the effect of sustainable luxury product communication focus on consumers' intention to buy, by revealing the mediating role of perceived quality. An experimental study has been carried out by using as a setting a page of a fictitious brand on the social network Instagram due to its current popularity subclassing other ones such as Facebook, Tok-tok or Twitter (Mediakix, 2021) to share visual contents and advertising posts, manipulating the type of communications to investigate consumers' sustainable consumption choices, and the effect of consumers' perceived product quality. Results show that the type of communication focus (internalized vs. externalized luxury) influences the perceived quality of the communicated product, which in turn has an effect on consumers' intention to buy. Thus, we firstly contribute to luxury research and practices by shedding light on how the luxury communication focus may influence consumers' sustainable consumption. Secondarily, we contribute to the literature about sustainable consumption increasing knowledge on how luxury products are becoming consistent with sustainable concepts and pro-environmental behaviors. Thirdly, we contribute to the literature about social media marketing by revealing how social media may be useful in proposing luxury communications with different focus stimulating sustainable consumption behaviours. Lastly, this research contributes to the literature on luxury values. Finally, managerial implications and future research lines will be provided.

Luxury Consumption: Internalized Versus Externalized Motivations
Traditionally, the consumption of luxury products is based on several factors, such as conspicuous consumption (Chaudhuri et al., 2011;Veblen, 1899), hedonism (Vigneron & Johnson, 1999), quality, uniqueness and durability (Sheth et al., 1991). On this basis, it is essential to consider the different facets relating to the behavior and motivations of luxury consumption. In this context, the literature on luxury marketing has consolidated the theory of self-determination theory as the basis of studies relating to the behavior and motivations of luxury consumption (Shao et al., 2019;Truong & McColl, 2011). According to Ryan and Deci (2000), the self-determination theory tends to conform to an approach on the motivations of consumption that focuses on behavior and personality development in social contexts (Truong & McColl, 2011). In this framework, motivational models that consider both social and individual factors can be considered (Colella et al., 2019;Vigneron & Johnson, 1999). With reference to motivational models based on social factors, in luxury consumption the importance of the perception that others have of the consumer is considered (Truong & McColl, 2011), which mainly signals one's wealth and status (Veblen, 1899). If we consider motivational models based on individual factors, however, in luxury consumption we consider the importance of the goals of self-fulfilment and individual style (Tsai, 2005). However, individual factors also include factors such as hedonism and experiential consumption (Müller-Stewens & Berghaus, 2014). On this basis, the most recent literature on luxury consumption has identified different approaches to luxury consumption, anchoring itself to the relationship between internal and external motivations (Eastman & Eastman, 2015;O'Cass & McEwen, 2004). In particular, Amatulli and Guido (2012) have underlined the luxury consumption dichotomy of externalized versus internalized luxury (Guido et al., 2020). Externalized luxury consumption has its roots in the theory of conspicuous consumption (Veblen, 1899). In this sense, the consumption of luxury goods relies on the constructs of materialism and ostentation (Belk, 1985;Richins & Dawson, 1992) and is aimed at indicating status and a social position to others (Guido et al., 2020;Amatulli & Guido, 2011Mason, 2001). On the other hand, internalized luxury consumption, bases its motivations on the more intrinsic side of consumers who are motivated by wanting to experience intimate motivations (Guido et al., 2020) and characterized by a low need for status (Han et al., 2010). In particular, in the context of internalized luxury consumption, consumers find personal satisfaction in the perceived product quality (Dubois et al., 2001;Truong & McColl, 2011). Therefore, internalized luxury consumption is rooted in personal and intrinsic motivations, such as expressing inner values, tastes, qualities, and individual style (De Angelis al., 2020).

Social Media Communication in Sustaining Luxury Type of Communication
Social media are online platforms useful to connect people to each other sharing ties, from casual knowledge, to working relationships, to family ties (Jiang et al., 2019). The procedures for accessing the social network are similar, based on registering a profile (generally for free) and on the possibility of adding contacts, inviting them to participate by selecting them from those who are already part of it, both for professional scopes such as in LinkedIn (Davis et al., 2020), and for personal purposes such as in Facebook, Instagram, Twitter, WhatsApp (Waterloo et al., 2018). An interesting factor for the marketers should be recognized into the ability of the virtual communities to act as an amplifier, through word-of-mouth news, trends and styles, thus allowing the development of different forms of viral marketing (Huang et al., 2019). Thus, today social media offers companies the opportunity to create web pages for marketing purposes and to communicated with their consumers (Colella et al., 2021;Jahn et al., 2012). Accordingly, social media marketing strategies consolidated its importance in the luxury sector too (Okonkwo, 2009). Regarding luxury consumers' motivations to use social media, Jahn et al. (2012) identify three main motives in terms of keep in touch and interacting with other consumers and with companies (Essamri et al., 2019;Kim & Ko, 2012); the acquisition, distribution, and co-creation of functional or hedonistic content (Hagtveded & Patrick, 2009;Phan et al., 2011;Vigneron & Johnson, 2004); and finally self-presentation, which is linked to the social context and personal identity (Jahn et al., 2012). Therefore, among the main motivations that push consumers of luxury products towards the use of social media is self-presentation, which is based on its dimension of visibility of luxury (Jahn et al., 2012). In this context, the studies specified what efforts social media marketing activities have been successfully implemented in the context of luxury (Colella et al., 2021;Kim & Ko, 2012;Godey et al., 2016). To illustrate, in order to positively influence consumers' luxury brands and products perception, in defining the best social media marketing strategy it is necessary consider five important to consider some fundamentals factors such as personalization, trend, positive WOM, interactions and thus communication with the target consumers (Godey et al., 2016;Kim & Ko, 2012). According to Phan et al. (2011), to develop an efficient marketing strategy aimed at improving consumers' perception of their products, luxury brands need to have a clear understanding of the concept of social media marketing potentiality and usable tools, e.g., social media posts and picture to communicate and interact with their consumers (Chu et al., 2013). A significant aspect that emerged from these studies is the level of interactivity that luxury brands have acquired in recent years (Colella et al., 2021), with particular regard to the interactivity that consumers have in the various decision-making processes in the purchase of luxury products. Kim and Lee (2019), argue that in the context of luxury consumption, the interaction involves the reproduction of those consumers who share, disseminate and defend their ideas, values, and experiences and who support brands and products (Kim et al., 2012). The disruptive process of digitization of the communication systems of companies plays an important role in which it needs to increase one's skills in the analysis of the relationship between luxury and consumers on the web (Amatulli et al., 2017). According to Okonkwo (2009), through social media, consumers often have the perception of being in full control of their choices, generating a particular form of apprehension on the part of the luxury brand (Godey et al., 2016). Therefore, modern luxury consumers are gradually turning their attention to social media platforms (Colella et al., 2021;Martín-Consuegra et al., 2019), and, according to Yu et al. (2017), activities carried out on social media platforms tend to increase consumer experience, brand engagement, interactivity, and brand loyalty, making companies' communication more accessible. By extension, such social media marketing strategies for luxury brands are becoming recurrent, especially to drive communication campaigns and advertising (see Colella et al., 2019 for a review). As a marketing strategy, several luxury brands are increasingly investing their marketing efforts towards digital communication, becoming pioneers in how they use various social media platforms (Heine & Berghaus, 2014), as for Burberry (as shown by Phan et al., 2011). Importantly, the social media advertising that disseminates messages and information about luxury brands tends to promote the purchase of luxury brands (Chu et al., 2019) and consumers-generated content are one of the most effective ways for interact with them via social media (Colella et al., 2021;Hasbullah et al., 2020). These contents shared via social media may have more influence than other sources, mainly because it is disseminated from a reliable source of information accumulated from a consumer's personal network (Castronovo & Huang, 2012). Based on this assumption, and on the luxury dicothomy scrutinized above, we hypothesize that: H1. The sustainable luxury product focus (Internalized Vs. Externalized) positively influences consumers' intention to buy sustainable luxury products.

Sustainable Luxury Consumption and Luxury Product Quality
Sustainable consumption is defined as "the consumption that supports the ability of current and future generations to meet their material and other needs, without causing irreversible damage to the environment or loss of function in natural systems" (Oxford Commission on Sustainable Consumption, 2000). Interestingly, consumers are becoming to be more attentive to sustainable consumption and their buying behaviour, in an attempt to alleviate the impact of their purchases on the environment (e.g., in Amatulli et al., 2021). By leveraging on such consumers' increasing concern for the impact of their consumption choices, most luxury brands have come to act in sustaining such forms of consumption (e.g., Athwal et al., 2019). However, Kapferer (2010) noted that luxury and sustainability are convergent because both focus on rarity, and high quality, due to consumers' growing interest in sustainability issues, scholarly research has been engaging in a very lively debate on sustainable luxury branding and consumption by demonstrating that sustainable luxury consumption has not a negative meaning (e.g., in Amatulli et al., 2017Amatulli et al., , 2021, but can maintain the same product quality standards while safeguarding the environment (Athwal et al., 2019). Despite the current increased consumers' attention of environmental issues and sustainable consumption, consumers who are concerned about the environment still remain uncertain about sustainable purchases due to the perceived lack of complete quality of some products (e.g., in Peattie & Charter, 2003).Indeed, if on the one hand, they prefer to buy green products because they do not damage or negatively affect the external environment, stimulating emotions such as "feeling proud" and an active part of environmental protection, on the other, they are wary of the higher costs of green products or perceived lower quality (D'Souza et al., 2017). Furthermore, researchers showed that the quality of products has a direct effect on the performance while also being closely linked with the satisfaction of the customers, their loyalty, and the intentions of repurchasing (Asgharian et al., 2012;Eskildsen et al., 2004). Accordingly, previous studies (e.g., D'Souza et al., 2017;Jaiswal & Kant, 2018) has shown that sustainable product quality moderates neither the relationship between attitude towards environmental issues and purchasing behavior, nor the relationship between information and purchasing behavior. Thus, marketers and managers should focus on the transparency and credibility of sustainable products and consumption, in the attempt to enable consumers to better understand the characteristics and usefulness of their products through appropriate communication focuses, by leveraging on the possible effects deriving from green product consumptions (Suki, 2016). Thus, we suggest that: H2. Consumers' perceived product quality mediate the relationship between sustainable luxury product communication focus (Internalized Vs. Externalized), and their intention to buy.
To clarify, our conceptual framework is provided in the figure below ( Figure 1). Figure 1. The proposed conceptual framework: The mediating role of consumers' perceived product quality

Methdology
With the aim of empirically testing our hypothesis, this study uses a quantitative approach. Thus, we developed the questionnaire for data collection. The questionnaire was created on the Qualtrics platform and was

Results and Discussion
To test our hypothesis, we ran the simple mediation model (Model 4) by Hayes' (2017) of the PROCESS macro for SPSS. The mediation model included the sustainable luxury product communication focus on the social media platform (internalized luxury condition = 1; externalized luxury condition = -1) as the dependent variable, consumers' intention to buy as an independent variable and the perceived product quality which acted as a mediator of the relationship between the independent variable and the dependent variable. First, we regressed the perceived product quality on the independent binary variable, and then we regressed consumers' intention to buy on the perceived quality and on the independent variable. Results showed a significant and positive effect (b = .31, t (130) = 2.41, p = .02) of the type of sustainable luxury product communication focus on consumers' perceived product quality. Furthermore, the perceived product quality had a positive and significant effect on consumers' intention to buy (b = 0.93, t (130) = 12.78, p = <.01). It is important to underline that the results revealed a non-significant direct effect (b = -.14, ns) of the sustainable luxury product communication focus on the consumers' intention to buy, but a significant and positive indirect effect of the independent variable on the dependent one through perceived quality (b = .29, 95% CI: .06,.53) (see Figure 2 below).

Figure 2. Results related to the simple mediaton model
Results demonstrate that consumers perceive a higher quality of sustainable luxury products when they are exposed to a communication message on the social media platform of a sustainable luxury brand that emphasizes ijms.ccsenet.org International Journal of Marketing Studies Vol. 14, No. 1; an internalized (vs. externalized) luxury consumption approach. In turn, consumers' greater perception of product quality leads to a higher intention to buy. These results supported our hypothesis. Moreover, for greater clarity of results we dabbed a Confirmatory Factor Analysis (CFA) to the different constructs considered in the study, finding satisfactory factor loadings and acceptable data fit (Hu & Bentler, 1999) (see Table 1). Although the results only point to an indirect effect of the sustainable luxury product communication focus on consumers' intention to buy (via perceived product quality), these findings offer support to our hypothesis by confirming that the perception of quality fully mediated the effect of the type of communication focus on consequent buying intentions.

Overall Findings
The purpose of this paper was aimed to investigate how the luxury product communication focus -in a social media research setting-may influence consumers' intention to buy, by shedding light on the mediator role of perceived product quality in influencing this relationship. Specifically, we exposed a sample of consumers to a communication message related to a sustainable luxury product, manipulating the communication focus (internalized vs. externalized), according to the definition of Amatulli and Guido (2011) which emphasizes an internalized (vs. externalized) approach to luxury consumption. Indeed, while internalized luxury refers to luxury consumption mainly driven by "internal" and ego-related motives, such as lifestyle and product quality, the externalized luxury refers to "external" luxury motives driven by consumers' status and price of the product. In this sense, consumers' perceived product could not be considered. Our results showed that higher perceived product quality denotes higher consumers' intention to buy, confirming that the type of attention to communication influences the perceived quality. Thus, the type of sustainable luxury product communication focus (internalized vs. externalized luxury) influences the perceived product quality, which in turn increases the consumers' intention to buy those products.

Theoretical Implications and Contributions
Theoretically, this study offers four main contributions to the literature. First, our results may advance knowledge of luxury research and practices by shedding light on how the sustainable luxury product communication focus influence consumers' intention to buy. Indeed, the results underline that sustainable luxury product communication focus can lead to higher green consumption values when the reasons for luxury consumption are mainly internalized (vs. externalized). Although several studies on luxury have focused on this dichotomy (Amatulli & Guido, 2012;Eastman & Eastman, 2015;Guido et al., 2020;O'Cass & McEwen, 2004), to the best of our knowledge, no studies previously focused on emphasizing communication focused on the motivational status of luxury consumers and how it may influence their buying intentions. Second, we extend the literature on sustainable consumption by increasing knowledge on how luxury products are becoming adaptable with sustainable concepts and pro-environmental behaviors. Furthermore, our results show that the perceived product quality can increase sustainable luxury consumption. Third, this research contributes to the social media ijms.ccsenet.org International Journal of Marketing Studies Vol. 14, No. 1; marketing literature by revealing how social media can be useful in proposing luxury communications by acting on different communication focuses to stimulate sustainable consumption behaviors. Indeed, the results show how social media platforms can become primary tools for communicating the sustainability of luxury brands and products. Particularly, through the sustainable luxury product communication focus on published posts (e.g., on social media), our results show how consumers with more intrinsic motivations for luxury consumption increase their intention to buy luxury products, especially for those consumers characterized by an internalized approach to luxury. Lastly, this research contributes to the literature on luxury product values, confirming that consumers' perceived product quality represents an important value for luxury consumers with extremely intrinsic values (Dubois et al., 2001) and, secondly, showing that this value can also be transmitted through a communication focused on social media platforms.

Managerial Implications
By considering our results, several marketing implications may derive. Firstly, luxury marketers and managers' efforts should be directed both to emphasize the communication focus and increase the quality perception of proposed products in consumers' minds, expecially regarding sustainable luxury products. Indeed, due to the complex combination of sustainability and luxury, consumers do not always perceive sustainable luxury products as being of high quality. Thus, communication campaigns should be directed to emphasize the quality hidden in sustainable luxury products too, making recognizable their unicity as a "perfect combination" able to bring closed two concepts traditionally far, such as luxury and sustainability, confirming the effectiveness of luxury brands' messages . Communicating product quality characteristic may be a winning strategy to reach those consumers luxury consumers, both typically reluctant toward such new luxury brand propositions, and led by externalized motivations in luxury consumption (Amatulli & Guido, 2011). Moreover, according to the luxury dichotomy (Amatulli & Guido, 2012), our findings may suggest how to reach consumers both led by luxury "internal" consumption motives, and "external" consumption ones. Indeed, while consumers characterized by "internalized" consumption motives typically seek lifestyle and product quality, the second one, is typically led by status satisfaction, and price. Accordingly, emphasizing sustainable luxury product characteristics may be useful both to satisfy those consumers looking for product quality in their consumption, and to incentivize those consumers looking for status, also in the attempt "to go green to be recognized" (Griskevicius et al., 2010). Furthermore, the results suggest that marketing and advertising activities on social networks should be more oriented towards responsible communication, emphasizing the advantages deriving from the consumption of sustainable luxury products in terms of improving the environmental impact, without however the intrinsic quality. Therefore, effective marketing strategies induce consumers to buy sustainable luxury products, and adopt respectful behaviors toward the environment, by leveraging on related psychological benefits, for example also by placing images that evoke nature, thus forming a positive image in consumers' mind, building a sustainable consumption image as better than traditional consumption (Peattie & Crane, 2003, 2005.

Limitations and Future Research
Despite the usefulness of our results, however, we acknowledge that this study has some limitations too. Notwithstanding the analyzed sample is representative, the results scalability may be limited. Moreover, some fundamentals variables characterizing luxury consumptions have been neglected and may be useful in deeply investigate consumers' behaviour. Thus, future studies could strengthen our study by shedding light on the possible role of some important luxury consumption-related characteristics (Colella et al., 2019) in terms of authenticity, quality, premium price, resonance, visibility, and prestige.