Dütting, PaulFischer, FelixParkes, David2017-04-192016Dütting, Paul, Felix Fischer, and David C. Parkes. 2016. Truthful Outcomes from Non-Truthful Position Auctions. In Proceedings of the 2016 ACM Conference on Economics and Computation, Maastricht, Netherlands, July 24-28, 2016.http://nrs.harvard.edu/urn-3:HUL.InstRepos:32227268We exhibit a property of the VCG mechanism that can help explain the surprising rarity with which it is used even in settings with unit demand: a relative lack of robustness to inaccuracies in the choice of its parameters. For a standard position auction environment in which the auctioneer may not know the precise relative values of the positions, we show that under both complete and incomplete information a non-truthful mechanism supports the truthful outcome of the VCG mechanism for a wider range of these values than the VCG mechanism itself. The result for complete information concerns the generalized second-price mechanism and lends additional theoretical support to the use of this mechanism in practice. Particularly interesting from a technical perspective is the case of incomplete information, where a surprising combinatorial equivalence helps us to avoid confrontation with an unwieldy differential equation.en-USConference Paper2017-03-1020162017-04-1910.1145/2940716.2940731