John,
You wrote "If the buyer is not happy he should contact the seller for a refund. If the refund is smooth then he should leave positive feedback"

I say NO, NO, NO. Getting money back does not necessarily mean the it was a positive experience. Just having to request a refund indicates there was a problem with the purchase. That is not a positive. In addition, most sellers will not refund shipping / handling so I may still be out money. Again, not a positive. I might not leave a negative feedback if the refund goes well but I certainly will not leave a positive feedback in that situation.
Paul