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

Take the unit back, you probably did not sell it for enough money that it makes a difference.  You can have the person send it to me for a look and repair as an option.  I can take a look and give you a repair estimate.  Or just take it back and list it for sale again.  It doesn't matter if he played it, it is not worth the money.  Have him pay for the return shipment and once you get it back without any other damage then refund the purchase price.

Just my $.02, but with the few unhappy buyers I've come across, I send a prepaid return tag and pay both sides of the shipping.  It's a small price to pay for the goodwill, and keeps your karma clean.  Make them happy and move on.

Though one can ascribe all sorts of chicanery to either party in a deal gone bad, it's been my experience that most buyers and sellers are pretty honest and straightforward. Disputes that I've been involved in have been more a matter of misunderstanding and lack of disclosure (my perception of "mint condition" may differ from yours) than outright dishonesty or fraud.
Your mileage may vary.  Best of luck sorting this out!

Though one can ascribe all sorts of chicanery to either party in a deal gone bad, it’s been my experience that most buyers and sellers are pretty honest and straightforward. Disputes that I’ve been involved in have been more a matter of misunderstanding and lack of disclosure (my perception of "mint condition" may differ from yours) than outright dishonesty or fraud.

It would be nice to think so, but unfortunately about 4% to 8% I’d estimate as scammers. It is too high of a price for many to pay for using eBay. I’ve got several stories too, one only turned out OK because of a detective in Warner Robins Georgia who took an interest, or I’d have been out several hundred dollars. It ended up being some 30-year-old guy living in his mom’s basement, and using her account, and no I’m not making this up, the detective told me.

If possible, arrange to pick up the returned item either at the post office or UPS or FedEx office to witness opening the box. The scammers send either an empty box, or with rocks, and then say you’re trying to scam them, with eBay of course taking their side. I’d also check, if you actually do get it back, to make sure it is the same serial number. I remember one story, a very rare item, the guy sends it, the buyer says not in as advertised condition, demands a refund and sends it back. Great, but the critical internal parts were missing.

I’m sorry to be the potential messenger of bad news, but this is the sad reality of eBay.

I saw you ad- it says as is and does not work. And the buyer is upset it does not work? Maybe a burned motor when the buyer tried to open the drawer. 
This buyer will make your life hell unless you take it back. 
I sell a fair amount on eBay and my experience is that if a buyer isn’t happy there’s virtually nothing you can do which will change that. So if the buyer isn’t happy I offer a full refund immediately. Occasionally, the response will be “but I want to keep it- can you refund part of the purchase price?” That’s a scammer and 99% of the time I say no to that however recently someone complained, I offered a full refund, and the person said- how about refunding $20. I figured it was a good way to be done with that buyer. It happened to be a person I’ve sold to before and he complained before and left “neutral” feedback- first time in 22 years I got other than positive feedback. 
He is now blocked 

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