  We characterize the statistical properties of a large number of agents on two
major online auction sites. The measurements indicate that the total number of
bids placed in a single category and the number of distinct auctions frequented
by a given agent follow power-law distributions, implying that a few agents are
responsible for a significant fraction of the total bidding activity on the
online market. We find that these agents exert an un-proportional influence on
the final price of the auctioned items. This domination of online auctions by
an unusually active minority may be a generic feature of all online mercantile
processes.
