If money is good, then shouldn't more money always be better? Perhaps not. Traditional economic theories suggest that money is an ever-increasing incentivizer. If someone will accept a job for US$20/hr, they should be more likely to accept the same job for US$30/hr and especially for US$250/hr. However, 10 preregistered, high-powered studies (N = 4,205, in the United States and Iran) reveal how increasing incentives can backfire. Overly generous offers lead people to infer "phantom costs" that make them less likely to accept high job wages, cheap plane fares, and free money. We present a theory for understanding when and why people imagine these hidden drawbacks and show how phantom costs drive judgments, impact behavior, and intersect with individual differences. Phantom costs change how we should think about "economic rationality." Economic exchanges are not merely about money, but instead are social interactions between people trying to perceive (and deceive) each others' minds.
Keywords: hidden motives; incentive backfires; incentives; irrationality; phantom costs.