Obvious Manipulations

A mechanism is strategy-proof if agents can never profitably manipulate, in any state of the world; however, not all non-strategy-proof mechanisms are equally easy to manipulate - some are more "obviously'' manipulable than others. We propose a formal definition of an obvious manipulation and argue that it may be advantageous for designers to tolerate some manipulations, so long as they are non-obvious. By doing so, improvements can be achieved on other key dimensions, such as efficiency and fairness, without significantly compromising incentives. We classify common non-strategy-proof mechanisms as either obviously manipulable (OM) or not obviously manipulable (NOM), and show that this distinction is both tractable and in-line with empirical realities regarding the success of manipulable mechanisms in practical market design settings.