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We conducted laboratory experiments for the multi-unit Vickrey auction with and without advice to subjects on strategy-proofness. The rate of truth-telling among the subjects without advice was 20%, whereas the rate increased to 47% among those who received advice. By conducting similar experiments for the pay-your-bid auction, which is not strategy-proof, we confirm that the increase in truth-telling owes significantly to the net advice effect, i.e., the effect beyond the so-called experimenter demand effect. Moreover, providing advice improves efficiency in the Vickrey auction, particularly in the early periods, when subjects are less experienced. It is well known that subjects tend to overbid in Vickrey auction experiments. Our results indicate the possibility that providing a piece of simple advice decreases such overbidding by promoting a better understanding of the strategy-proofness property in the Vickrey auction. Strategy-proof mechanisms are sometimes criticized because players often fail to find the benefit in telling the truth; however, our observations show that introducing advice on the property of strategy-proofness helps them behave “correctly.”

January 2019. Revised November 2019., 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.”