This article is from the eBay FAQ, by William B. Shaw firstname.lastname@example.org with numerous contributions by others.
Sellers who bid on their own auctions or have a closely related party bid on
their auctions without any intention of winning are engaging in shill
bidding. Shill bidding is done to increase the final price for auctions or
to make an auction appear more popular than it really is.
With the changes eBay has made restricting access to email addresses and
other member information, it is becoming increasingly difficult to detect
this type of activity. If you see the same bidder in the bid history for
many of a seller's auctions or a high number of bid retractions, these are
indications (not guarantees) of shill bidding.
If you suspect shill bidding, but aren't sure, post the auction link to amoe
and let the group help.