The network layer operations in ad hoc networks - namely packet routing and forwarding - are solely performed by the nodes themselves and consequently rely on the cooperation among them. In such networks, to best manage packet forwarding to the aimed destination node raises a need for continuous monitoring of the network service that is likely to be obtained from the other node cooperation. In this paper, we survey reputation mechanisms based on forwarding monitoring in ad hoc networks and we identify and analyze the relevant issues concerning the evaluation of forwarding operations. Finally, we highlight the need for transposing these results to hybrid ad hoc networks, with the aim to monitor the availability of the Internet access.