Why is it not possible to leave a negative feedback for a buyer? This is totally biased. Not good enough for eBay to give them a strick. When they are totally banned, nothing to stop them from starting up another account. It is not too difficult.
why do you want to give them a negative anyway? if they didn't pay just open a non payment dispute and close it in 4 days they will receive a stirke on their account.If they receive a few of these they will be blocked from sellers. If you give them a neg what to stop them closing their account an opening another?
