Does any one have any experience with sellers using shill bidders to bid up the price of an item,

[rose-dee]

Not that I've ever been able to prove, but if you suspect this is happening, you should report it to eBay.  It is not only against eBay rules, but is illegal in the "real world" too. 

[karl*katz]

Shill bidding policy

http://pages.ebay.ca/help/policies/seller-shill-bidding.html