Using information–cognition–intention model and by comparing emotional and rational negative word-of-mouth (nWOM), this study considered nWOM’s role in online flash sales by examining whether consumers would find nWOM diagnostic and lower purchase intentions during flash sales. Partial least squares analysis of 308 questionnaires (150 for emotional and 158 for rational nWOM) revealed that worry, skepticism, and optimism emotions resulting from reading nWOM played a more limited than those of gratitude. Perceived diagnosticity of rational nWOM dampened while emotional nWOM did not dampen purchase intentions. Hence, nWOM content influenced whether nWOM acted as a brake on purchase intentions.