I guess they could hunt them down, slam them against the wall and take the $.  Or, as have been suggested previously, before anybody was allowed to bid they would have to pay bond.  However, if I was told that I am not allowed to bid unless I pay something up-front, I would have never started to buy on eBay.

Actually, I think the way it is works pretty well; it is up to each seller to decide if they allow non-payers to buy from them, and how many strikes they think is OK.  It would work even better if all sellers would go through the disputes, and had some blocks in place.