[drcy]

As mentioned, someone could innocently enter the wrong amount and retracted it, but, presumably, would soonafter enter another, correct bid.

Blocking someone due to a single retraction seems too much for me (especially if they have $$ to spend on your items), but it's your auctions and your choice.

As far as nefarious bid retractions go, the issue usually isn't a once in a while bid retraction but a lot of them. If it's your item, your auction and you don't know the person, obviously he isn't a shill bidder.