"but it's best to buy from sellers who frequently sell items and have recent, positive feedback " ... like two of UOForums sponsors .... RPG-Bay and UOTreasures

Agree that you should look for precentage of total positive and recent feedbacks (the higher number of total feedbacks the better) and there is a way to stop them if they do take your cash and not deliver the goods. (chargebacks and stop payments plus reporting them for fraud with ebay/paypal)

They in turn will want to check you out as well if you are a new ebayer or someone with a low amount of feedback even if all postitves. If you only have a few 'purchases' they as well want to make sure you don't take their goods and not pay.

Also, check that they have stated how to reach them - plus you can send them an email through ebay to ask the seller a question ... if they provide an IM you can do a search for them as well ... like icq search by uin. Thats another way you can verify their existance.

Good Luck ...