Corrupt third parties undermine trust and prosocial behaviour between people.

Corruption is a pervasive phenomenon that affects the quality of institutions, undermines economic growth and exacerbates inequalities around the globe. Here we tested whether perceiving representatives of institutions as corrupt undermines trust and subsequent prosocial behaviour among strangers. We developed an experimental game paradigm modelling representatives as third-party punishers to manipulate or assess corruption and examine its relationship with trust and prosociality (trust behaviour, cooperation and generosity). In a sequential dyadic die-rolling task, the participants observed the dishonest behaviour of a target who would subsequently serve as a third-party punisher in a trust game (Study 1a, N = 540), in a prisoner's dilemma (Study 1b, N = 503) and in dictator games (Studies 2-4, N = 765, pre-registered). Across these five studies, perceiving a third party as corrupt undermined interpersonal trust and, in turn, prosocial behaviour. These findings contribute to our understanding of the critical role that representatives of institutions play in shaping cooperative relationships in modern societies.