Reputation models in mobile ad hoc networks are confronted with the problem of strategically reporting dishonest recommendations given by a selfish group whose purpose is to maximize its benefit. To solve this problem, a truthful and group strategyproof reputation mechanism based on cooperative game theory is proposed in this paper. We first study two supermodular total compensatory payment functions. On the basis of the selection game, we construct a corresponding indirect revelation mechanism and a direct revelation mechanism called claiming compensation mechanism, which is proved to be group strategyproof. Then we choose the extended Shapley value as the concrete compensatory payment scheme and propose an algorithm to generate possible outcome groups for the claiming compensation mechanism. Simulation results show that when we use the total compensatory payments function, which does not relate to cost values, the proposed mechanism is group strategyproof. Finally, all possible situations for a liar are demonstrated and discussed. Copyright © 2014 John Wiley & Sons, Ltd.