haha i have similar problems, i dont think it can be avoided.. other then refusung to sell to the buyer, put a clause in the listing, payment must be recieved within 7 days (unless arangements made) otherwise failure to pay blah blah blah
one thing that bugs me is when you buy something and pay instanly they dont leave feedback till after you have received the item and left feedback for the seller, now i just dont leave them feedback till they have left it for me paying promptly.....
i have probably had about 50 people fail to leave feedback over the years on eBay... it is still frustrating every time.