The Impact of Social Proof on Consumer Purchases in E-Commerce: A Literature Review of Four Credibility Mechanisms

Consumers in e-commerce environments increasingly rely on social proof, the tendency to look to others’ behavior when making decisions under uncertainty, rather than independent product evaluation. However, existing research often treats social proof as a single construct without distinguishing how its different forms operate. This literature review synthesizes a corpus of eight recent empirical and conceptual sources to examine how four distinct categories of social proof (influencer endorsements, user-generated content (UGC), peer endorsements, and expert testimonials) influence consumer trust, brand perception, and purchase intention in online commerce. Sources were gathered through searches of Google Scholar, the SSRN and ResearchGate repositories, the AIS Electronic Library, and academic journal websites, with all included sources published between 2015 and 2025. The review finds that each category operates through a distinct psychological mechanism, grounded respectively in parasocial interaction, informational social influence, social comparison, and source credibility and signaling theory: influencer endorsements work through perceived authenticity and relational closeness, UGC through collective peer validation, peer endorsements through perceived similarity and reduced psychological distance, and expert testimonials through authority and institutional legitimacy. The review further proposes, as a central proposition for future testing rather than an established finding, that layered combinations of peer and expert signals may amplify bandwagon effects by confirming that a product is both widely adopted and professionally validated. These findings offer a structured framework for researchers and practical guidance for managers, including prioritizing micro-influencer authenticity, displaying verified user-generated content, and pairing peer recommendations with expert certifications to strengthen credibility and increase purchase intention.