How to Block an eBay Customer
If you've had a bad experience with a particular customer on eBay and you don't want that person to be able to bid or buy your items in the future, you can set up a bidder block for his or her User ID. If you block bidders, they can't bid; eBay tells them that they have to contact you by e-mail before their bids will be accepted.
You can add or delete bidders from your list at any time. eBay has managed to make the page a little hard to find; try going directly to the Buyer/Bidder Management area.
If the buyer's feedback profile provides any indication that the buyer has gone AWOL in the past, start thinking about getting out of the transaction before too much time passes. If the buyer looks to be on the level, continue to give him or her the benefit of the doubt.