Pseudonyms in Cost-Sharing Games

This work initiates the study of cost-sharing mechanisms that, in addition to the usual incentive compatibility conditions, make it disadvantageous for the users to employ pseudonyms. We show that this is possible only if all serviced users pay the some price, which implies that such mechanisms do not exist even for certain subadditive cost functions. In practice, a user can increase her utility by lying in one way (misreport her willingness to pay) or another (misreport her identity). We prove also results for approximately budget-balanced mechanisms. Finally, we consider mechanisms that rely on some kind of "reputation" associated to the pseudonyms and show that they are provably better.