BidderBlock

From HammerTap:

Like it or not, every eBay seller knows of bidders he or she would rather not have bidding on his or her auctions. BidderBlock allows you to create, maintain, and share a list of bidders who are blocked from participating in your eBay online auctions. Add and delete bidders from your list with ease, and view detailed information about the buying and selling history and feedback of any bidder on your list. Send messages automatically through eBay to any bidder you've added or removed from your list. Export and import lists to share with other users. Add others' lists to your own - you can place up to 1000 user IDs on your blocked bidder list to achieve maximum protection from problem bidders. BidderBlock works on all the international eBay sites and can update itself automatically.