A strategy-proof mechanism should be announced to be strategy-proof: An experiment for the Vickrey auction

We conduct laboratory experiments for the Vickrey auction with and without an announcement on strategy-proofness to subjects. Although the rate of truth-telling among the subjects stays at 20% without the announcement, it increases to 47% with the announcement. Moreover, by conducting experiments for the pay-your-bid auction, which is not strategy-proof, with and without advice, we find that our experimental results are not attributed to so-called experimenter demand effects. Strategy-proof mechanisms are sometimes criticized because players often fail to find the benefit of truth-telling, but our observations tell that introducing an educative announcement helps them behave "correctly".