Despite the potential for market domination and power abuse, it is also true that big businesses enhance consumer choice, job benefits, and welfare. Yet, big businesses are sometimes portrayed as inherently bad. Why? And does it matter for how we treat these organizations as decision-makers? Informed by moral typecasting theory, we suggest people are less likely to perceive big businesses as a vulnerable victim than small businesses, making it seem more acceptable to cheat them for selfish gain. We studied this ‘business-size bias’ across 7 experiments (USA). Experiments 1a-c (N=2,556) found that people intended to be more dishonest against big than small businesses, mediated by lower vulnerability perceptions. Experiments 2a-c (N=1,561) found that people also behaved more dishonestly toward big businesses. Experiment 3 (N=592) replicated the business-size bias in dishonesty, and found that it was mediated by perceptions of big businesses as less vulnerable and less moral than small businesses.