After they made a payment I would ask for a photo-copy of their ID, or to wait 3-days to make sure the payment went through properly (Paypal's normalized way of handling this was to mark the Payment as confirmed leaving the seller thinking everything was okay only to reverse it say 3 days later, screwing the seller). If I recall one of the buyers even offered to try a different account when I told them the payment got flagged.
In about a week's time I had received $5000 or so worth of transfers (all of them from stolen accounts!) Subsequently Paypal froze my account. I never was able to sell that World of Warcraft account either.