I sold a CAL Aria Tube CD player and buyer claims a burning smell

I’m sure there’s something burning over there but it ain’t your player. 

I am sorry this is happening to you.  After reading all the responses, if it were me I would offer the refund contingent upon the safe return and inspection of your player.  And, I would open it in front of a neutral 3rd party as mentioned above.  Good luck!

I’m with the people who think that the buyer is a scumbag fishing for a partial refund and wants to keep it because there’s nothing actually wrong. I’ve been selling on eBay for 20 years and have perfect feedback and have seen my fair share of this tomfoolery. 

Offer the refund but make it contingent upon safe and timely return of the product and see what they say.

I’ve sold and bought stuff on eBay for years, not a ton volume wise, but including some high value electronics, a car, and a few motorcycles.  In the description in all caps I put, “SOLD AS IS, NO RETURNS,” though sometimes I’ll offer a DOA warranty of one business day.  Luckily, I’ve never had a problem, but I’ve never sold a non-working item.  Bottom line is, you disclosed the condition and terms of no returns.  I’d stick with it, sometimes you got to take a stand when you’re right.  You get to respond to negative feedback, right?  You just might be warning off some other people from this a**hole., though not likely.  Not every seller loses in a dispute.