Decoy ballots do not count in election outcomes, but otherwise they are
indistinguishable from real ballots. By means of a game-theoretical model, we
show that decoy ballots may not provide effective protection against a
malevolent adversary trying to buy real ballots. If the citizenry is divided
into subgroups (or districts), the adversary can construct a so-called "Devil's
Menu" consisting of several prices. In equilibrium, the adversary can buy the
real ballots of any strict subset of districts at a price corresponding to the
willingness to sell on the part of the citizens holding such ballots. By
contrast, decoy voters are trapped into selling their ballots at a low, or even
negligible, price. Blowing up the adversary's budget by introducing decoy
ballots may thus turn out to be futile. The Devil's Menu can also be applied to
the well-known "Lemons Problem"
