This paper explains and tests empirically why people employed in product promotion are less willing to trust others. Product promotion is a prototypical setting in which employees are mandated to express attitudes that are often not fully sincere. On the basis of social projection theory, we predicted that organizational agents mandated to express insincere attitudes project their self-perceived dishonesty onto others and thus become more distrustful. An initial large-scale, multi-country field study found that individuals employed in jobs requiring product promotion were less trusting than individuals employed in other jobs—particularly jobs in which honesty is highly expected. We then conducted two experiments in which people were tasked with promoting low-quality products and either were allowed to be honest or were asked to be positive (as would be expected of most salespeople). We found that mandated attitude expression reduced willingness to trust, and this effect was mediated by a decrease in the perceived honesty of the self, which, in turn, reduced the perceived honesty of other people. Our research suggests that the widely used practice of mandating attitude expression has the effect of undermining an essential ingredient of economic functioning—trust.