That's one method eBay provides for blocking certain bidders. Additionally, you can ban specific users from your auctions. To do this, you have to email the user telling him or her not to bid on your auctions, and cc SafeHarbor--which, in turn, will help enforce your request. If the person bids on your auction, he or she is subject to suspension. However, there's no specific program in place to automatically block the bid, and SafeHarbor doesn't always enforce it. One OAUA user requested a bid block but SafeHarbor let the person bid "just this once." The person bid, caused trouble, and left the seller negative feedback. eBay did eventually remove the feedback and warned the bidder, but the auction had closed and the seller was out the time and effort involved in relisting the auction.

Other Sites' Perspectives
Amazon.com Auctions sellers have asked for the option of blocking bidders but they currently don't have access to such a feature. Instead, they rely on site policy enforcement to resolve problems with bidders. "I have been selling on Amazon.com almost since the beginning of Amazon.com Auctions and have had very few problems," reported one user. "Since I started taking Amazon.com 1-Click, most folks pay. If folks bid and don't pay, I notify Amazon.com and let them deal with deadbeats."

At eHammer, a high-end antique-focused venue, if enough folks complain about a user, the site will remove the user. This seems to be the status quo at auction sites that don't offer a bid-blocking feature.

eHammer encourages users to work things out privately. Phillip Rinehart of eHammer says that to install a bid-blocking feature at the site "goes against the grain of keeping an open playing field." According to Rinehart, eHammer hasn't had a huge need for a bid-blocking feature because its volume and user base are significantly less than that of an eBay or Yahoo Auctions. "It's easier to be anonymous at a site with many millions of users," he said. "At eHammer, it's easier to keep an eye on things. If and when we ever have the kinds of problems that would make a bid-blocking feature necessary, we'd probably add one."

Some sites that offer high-end items will allow sellers to block bids from certain users, but the matter is handled privately between the seller and the site administrator. With business-to-consumer auction sites, problematic users are simply removed, thus blocking future bids. Other sites handle the matter similar to eBay: They'll ask you to email the bidder with the request to refrain from bidding on your auction and to cc the site administrator. If the bidder bids on your auction, he or she is subject to suspension.

Disadvantages
If the bad experience that made a seller block a bid was a misunderstanding, the seller may be losing a potential steady customer. One could argue that the bidding pool is big enough at eBay to not have to worry about it, but this also depends on what products you sell. If the market is small, it's better to resolve disputes than burn bridges. If you sell wildly popular items, the risk isn't as great.

Bid blocking is obviously a bigger issue at high-traffic sites, which is why they make provisions for it. As other online auction sites grow in popularity and attract their own gaggle of problematic users, they'll have no choice but to offer the feature as well.

Handling Bid Retractions Understanding Feedback Avoiding the Buy and Switch