I've seen a lot of auctions where the seller (1) forbids buyers with less than so and so feedback from bidding, and (2) lectures buyers (in the description) that he expects winning bidders to pay, that he will put in for, with eBay, a final value percent credit if he is not paid, will leave neg feedback, etc.

You can ask your question on eBay's Feedback Discussion Board, and you will get lots of replies and suggestions. Some people practically make a hobby of hanging around and posting to those discussion boards. Look here:
http://forums.ebay.com/db2/forum.jspa?forumID=113

Robert