From image to action: How social proof turns brand image into repurchase intention

This study examines how social proof shapes the relationship between brand image and repurchase intention in an emerging digital marketplace, distinguishing three forms that operate through different mechanisms: user-generated content, brand ambassadors, and testimonials. Because online markets involve considerable information overload, consumers rely heavily on others' evaluations to reduce decision risk; however, forms of social proof vary in authenticity and persuasive effectiveness, and prior research has largely treated them as a single, uniformly positive construct. A two-study, mixed-methods design set in Vietnam addresses this gap. Study 1 applies a Vietnamese-optimized RoBERTa (Robustly Optimized BERT Pretraining Approach) model to social media comments to surface authentic consumer sentiment, providing exploratory, triangulating context without constituting a direct hypothesis test. Study 2 tests the proposed relationships using moderated regression on survey responses from 394 active Vietnamese online shoppers. Results show that brand image exerts a strong positive direct effect on repurchase intention. User-generated content significantly strengthens this relationship, with the largest effect among consumers holding moderate brand-image perceptions. Brand ambassadors moderate the relationship but show a bounded pattern, with diminishing influence once brand image is already strong. Testimonials exert a dual effect: they amplify the brand image-repurchase link when perceived as credible, but, when seen as commercially motivated, they independently trigger skepticism and weaken repurchase intention. By conceptually and empirically distinguishing ambassadors from testimonials, this study shows that social proof is not a uniformly positive force but a context-dependent mechanism conditioned by authenticity, with implications for transparency-oriented digital marketing strategy.