eBay has a very clear policy on allowing sellers to cancel bids from buyers they are not comfrtable with. If, because of an unsatisfactory feedback profile, or some other valid reason (not racial or other descrimination, but a reason based on the user's transaction history or email communications), a seller wishes not to sell to a particular user, the seller can cancel the bid, email the bidder and request that he not bid again.

If the bidder continues to place unwanted bids on the seller's auctions, the seller can contact SafeHarbor, who will then warn the bidder, or suspend him if the unwanted bidding persists.

It stands to reason that the purpose of the Feedback system is to let users know the history of users, and if the information in the feedback profile tells a aseller that this is a problem bidder, then of course the seller can refuse to deal with the buyer.

I had one psycho bidder (who had 15 completed transactions, received 15 positive feedbacks, and then had had left 15 negative feedbacks relating to "rampant capitalism on eBay) persist on bidding on my auctions after I cancelled hteir bids and told them not to bid again, and SafeHarbor NARU'd them within one hour of my complaint.