Live streaming has emerged as a critical channel for connecting farmers with markets. However, the majority of farmers lack e-commerce operation experience, often presenting awkwardly and expressing themselves inadequately during live streaming, which significantly hinders sales performance. Virtual streamers, with their characteristics of round-the-clock availability and extensive knowledge reserves, inject new momentum into agricultural live streaming. Nevertheless, how to efficiently leverage virtual streamers to expand sales channels remains a key issue requiring urgent resolution. Based on the source credibility theory and trust transfer theory, this study focuses on the influence of virtual streamers’ source credibility (i.e., trustworthiness, expertise, attractiveness, similarity) on purchase intentions in agricultural live streaming, and explores the mediating role of swift trust and the moderating effect of platform reputation. An analysis of 607 valid questionnaires reveals that virtual streamers’ source credibility has a positive impact on purchase intention, with swift trust playing a mediating role in this relationship. Moreover, platform reputation not only positively moderates the effect of virtual streamers’ source credibility on swift trust but also moderates the effect of swift trust on purchase intention. Additionally, fuzzy-set qualitative comparative analysis (fsQCA) identifies five configurational paths that trigger high purchase intention. This research expands the research perspective on virtual streamers in agricultural live streaming and provides theoretical references and practical guidelines for optimizing the application strategies of virtual streamers in agricultural live streaming.