Do you have blocks in place so that buyers with 2 or more non paying strikes in the last 12 months can't bid on your items? Having blocks is far more beneficial than being able to leave negative feedback. You can't stop buyers with negative feedbacks from bidding/buying, but you can stop them if they are habitual non payers.

Let the group know if you don't have blocks in place and need a hand to set them up, and someone will gladly help you. The more people that have these blocks in place, the better eBay will become, as these people will get sick of not being able to buy from a lot of sellers and either open a new account (which can also prevent them from buying from a lot of sellers), or they just give up.