In two studies, we tested the power of revenge as a justification mechanism that enables people to cheat with a clear conscience. Specifically, we explored the effects of prior dishonesty and unfairness towards participants on their subsequent moral behavior, as well as the physiological arousal associated with it. To this end, we employed a two-phase procedure. In the first phase, participants played one round of a bargaining game (the Ultimatum game in Study 1 and the Dictator game in Study 2) in which we manipulated whether the players had been treated (un)fairly and (dis)honestly by their opponent. In the second phase, they did a perceptual task that allowed them to cheat for monetary gain at the expense of their opponent from the first phase. In Study 1, participants also took a lie detector test to assess whether their dishonesty in the second phase could be detected. The behavioral results in both studies indicated that the opponent’s dishonesty was a stronger driver than the opponent’s unfairness for cheating as a form of retaliation. However, the physiological arousal results suggest that feeling mistreated in general (and not just cheated) allowed the participants to get revenge by cheating the offender while dismissing their associated guilt feelings.