Walrasian tatonnement has been a fundamental assumption in economics
ever since Walras' general equilibrium theory was introduced
in 1874. Nearly a century after its introduction, Vernon Smith relaxed
the Walrasian tatonnement assumption by showing that neoclassical
competitive market theory explains the equilibrating forces in "double-auction"
markets. I make a next step in this evolution by exploring
the predictive power of neoclassical theory in decentralized naturally
occurring markets. Using data gathered from two distinct markets-
the sports card and collector pin markets-I find a tendency for
exchange prices to approach the neoclassical competitive model prediction
after a few market periods.