In this paper we address the question of collusion in mechanisms under asymmetric information. We develop a methodology to analyze collusion as an informed principal problem. First, if collusion occurs after the agents accept or reject the principal's offer; the dominant-strategy implementation...

We investigate the issue of implementation via individually rational ex-post budget-balanced Bayesian mechanisms. We demonstrate that all social choice rules that generate a nonnegative ex-ante surplus, including ex-post efficient ones, can generically be implemented via such mechanisms for any...