A dynamic model with many sellers and many buyers is constructed, in w
hich buyers who fail to purchase in the current period may attempt to
purchase in the future, and sellers who fail to sell may sell in the f
uture. An equilibrium is found where sellers hold identical auctions a
nd buyers randomize over the sellers they visit. Auctions alter the di
stribution of buyer types by removing high value buyers more rapidly t
han low value buyers, and an equilibrium distribution of buyer types i
s constructed. Sellers in equilibrium post an efficient reserve price
equal to the sellers' value of the good, and an auction with efficient
reserve is an optimal mechanism from each seller's point of view, in
spite of the ability of any seller to alter the distribution of buyer
types participating in the seller's mechanism by altering the mechanis
m.