“Marks on the underside”

You shoud have mentioned it, and used photos.  But beware, he may have swapped drivers on you.

Buyer's wife saw the cost on a CC statement.....

Buyer was a reseller/flipper who realized he could not flip for a profit...

Buyer wanted to play for a few days and then return....

Reason really does not matter.  Ebay allows returns for ANY REASON STATED BY THE BUYER.

It does not matter if you list "AS-IS", No Returns etc.  If the buyer wants to return the item, Ebay will allow the return.  They want to compete with Amazon and their no questions asked return policy.

OTOH Ebay provides the largest audience, and generally results in more completed sales.  My experience is Ebay results in more sales for me than any other venue.  USAM is a distant 2nd.  With a wider audience, comes the fact you are dealing with everybody.  The chance of encountering an unethical buyer increases accordingly.

Include lots of Hi Resolution Pictures.  Include a very detailed description.  If there is a minor flaw, describe it in detail.

Good thread and reposting this as it applies here as well - I recently ly had one member here on Audiogon just a few months ago buy an expensive interconnect cable from me owned it for about 10 days and then decided that the cable was "broken'' and wanted his money back. Needless to say that this created an issue with Pay-Pal who really looked at both sides of this situation in which I had to literally defend myself and get verification from the cable manufacturer on why the cable as the buyer described it was in fact not broken but a product / result of his own equipment's shortcomings. This member / provided no information to Pay-Pal support to support his allegation ( hmmm sound familiar ) about the cable being '' broken '' and after about 6 weeks Pay-Pal ruled in my favor. He said ( lied ) that is was broken just to get his money back because he didn't like the sound. I now put ; No Returns on my adds just is case anything like this happens again. If you don't like it is your responsibility to re-sell it - not mine !        

IF you did not mention the marks your wrong.