  We study the bilateral trade problem: one seller, one buyer and a single,
indivisible item for sale. It is well known that there is no fully-efficient
and incentive compatible mechanism for this problem that maintains a balanced
budget. We design simple and robust mechanisms that obtain approximate
efficiency with these properties. We show that even minimal use of statistical
data can yield good approximation results. Finally, we demonstrate how a
mechanism for this simple bilateral-trade problem can be used as a "black-box"
for constructing mechanisms in more general environments.
