Manufacturers, digital platforms, and marketing researchers frequently seek to understand consumer preferences to inform product design, customer profiling, and personalized recommendations. A common method for eliciting such preferences is to present consumers with a list of predefined options and ask them to “check all that apply.” Although this approach is widely used in surveys, online registrations, and recommendation systems, little is known about the cognitive process underlying how consumers interpret and respond to these tasks. Across studies, we find that consumers rely on a small subset heuristic—a strategy based on the assumption that only a limited proportion of available options can be genuinely liked. Rather than expressing stable preferences, consumers selectively endorse a small minority of items, typically representing 20–40% of those presented, with the number of selections scaling proportionally with the choice set size. This heuristic reflects an underlying assumption that preferences exist along a continuum from strong dislike to strong like, and only a few options merit positive endorsement. The effect is robust across contexts and attenuates when external incentives or goals override default decision tendencies. These findings reveal a systematic heuristic in preference elicitation and carry important implications for survey design, consumer profiling, and algorithmic recommendation systems that depend on self-reported preferences.