Brian covered it.
It's a questionable tactic. If the shill outbids everyone, then even in the product doesn't change hands, fees still need to be paid. So if the tactic doesn't work and the high "selling" price doesn't result in driving the market up, the seller is out of pocket for nothing. In addition, I believe it's against eBay's policies. If they find out about it, the seller's account can be terminated.
I am pretty sure that if you are shill bidding for yourself both of "you" could just agree not to have a sale and then all but the listing fees are reinstated.
(I did some research with a fellow knife ebayer after I am sure a shill bid was used on me.)
