This article explores how consumers’ bounded rationality can justify antitrust intervention when a firm becomes a monopoly and exploits a product attribute that was not policed by market forces when there was competition for the market. Behavioral economics predicts product complexity leads consumer demand to be a function of salient costs and benefits rather than of actual costs and benefits of products. The divergence between the former and the latter hinders and distorts competition. In fact, comparison shopping is costlier, and sellers can backload part of their prices to nonsalient product attributes. Consumers perceive only a distorted lower price by focusing on salient product features, which leaves room for inefficient matching and opportunistic behavior given the risk of ex post exploitation. These are behavioral limits of competition. In this work, I argue that when (i) there is a lock-in problem, (ii) consumers do not control the probability of triggering a hidden price, and (iii) a typical consumer could not have reasonably expected to find such a hidden price, antitrust intervention would not only deter ex post exploitation but would also enhance competition on the real price of goods. Antitrust would correct a behavioral market failure.