Apparently, ebay has now made it so that if somebody bid on your auction and then did not pay for it and left you negative feedback, you now can send in a request to ebay to have the feedback removed and it will be removed.

This very good move takes away the possibility of harassment by competitors who have multiple accounts that they use for malicious purposes.  They won't be able to permanently damage your feedback rating.

You should also google auction collection agency to find some of the companies who will act as collection agencies for your non-paying bidders.  If enough people implement collection agency language in their auctions and then follow through with non-paying bidders, the non-paying bidders can end up with getting their credit score ratings affected after conducting themselves in a malicious manner.