EBay allows you to auction off new and used items, ebooks, and various services. Unfortunately, not all buyers are created equal -- some may continuously try to buy your stuff, only to fall through on the payment. Others may purchase only to leave negative feedback, whereas others may send you harassing messages or comments. Fortunately, you can use eBay's blocking feature to prevent these people from bidding on anything you put up for sale. Unfortunately, this feature can be a little tricky to find, as you have to know the correct link to use.
Go to "Blocked buyer/bidder List" by copying and pasting the following link:
Type in the user ID of the eBay member you want to block from buying your merchandise.