  We study the robust double auction mechanisms, that is, the double auction
mechanisms that satisfy dominant strategy incentive compatibility, ex-post
individual rationality, ex-post budget balance and feasibility. We first
establish that the price in any deterministic robust mechanism does not depend
on the valuations of the trading players. We next establish that, with the
non-bossiness assumption, the price in any deterministic robust mechanism does
not depend on players' valuations at all, whether trading or non-trading, i.e.,
the price is posted in advance. Our main result is a characterization result
that, with the non-bossiness assumption along with other assumptions on the
properties of the mechanism, the posted price mechanism with an exogenous
rationing rule is the only deterministic robust double auction mechanism. We
also show that, even without the non-bossiness assumption, it is quite
difficult to find a reasonable robust double auction mechanism other than the
posted price mechanism with rationing.
