The actual behavior of third parties disconfirms the hypothesis that they care only about their own economic payoffs and thus will never punish (Fig. 1). Most third parties punished dictators who transferred less than half their endowment, and the majority of recipients expected them to do so. At each transfer level below 50, roughly 60% (n = 22) of players C chose to punish the dictator A, and with the exception of transfer level 40, the proportion of recipients B who expected C to punish was higher than the proportion who actually did so.

Builds on: "Unaffected bystanders punish norm violators even without personal stakes"

Ernst Fehr, Third-Party Punishment and …, loc. 29