This study investigates the impact of platform-issued "quick-seller" certificates (indicating sellers with faster dispatch than others) on buyers' postpurchase behavior. Drawing upon the theoretical lens of psychological contract violation (PCV), we hypothesize the effects of quick-seller certificates on order cancelations, as well as the subsequent impacts of cancelations associated with the quick-seller certificates on buyers' future purchase frequency and search behavior. Using a comprehensive transaction dataset, the study reveals that quick-seller certificates increase the likelihood of cancelation of an order. Furthermore, we also find that an order cancelation from a certified quick seller results in decreased purchase frequency and a higher incidence of product comparisons through search engines.