  In a seminal paper, McAfee (1992) presented the first dominant strategy
truthful mechanism for double auction. His mechanism attains nearly optimal
gain-from-trade when the market is sufficiently large. However, his mechanism
may leave money on the table, since the price paid by the buyers may be higher
than the price paid to the sellers. This money is included in the
gain-from-trade and in some cases it accounts for almost all the
gain-from-trade, leaving almost no gain-from-trade to the traders. We present
SBBA: a variant of McAfee's mechanism which is strongly budget-balanced. There
is a single price, all money is exchanged between buyers and sellers and no
money is left on the table. This means that all gain-from-trade is enjoyed by
the traders. We generalize this variant to spatially-distributed markets with
transit costs.
