Inceptions
It doesn't matter what the buyer's feedback score is, the action you need to take is the same.
After 4 full days after the sale, cancel the transaction for non-payment so the buyer earns an unpaid item strike on his account.
You can block the buyer here:
http://pages.ebay.com/services/buyandsell/biddermanagement.html
Also, scroll down on that page and turn on the auto-block for buyers with 2 or more unpaid item strikes within 12 months for more protection.
