Bid Troll

Someone who Bids huge amounts for an item on eBay with no intention of paying either for a joke or to end your item as it is competing with their's.

John: Did you hear about those AK47 £5 notes going on eBay for £80,000.
Joe: No one actually paid 80 grand for a £5 note, it was just bid trolls racking up the price for a laugh.