What to do when buyer claims sellers item broken?

Thanks for all the suggestions. I will first ask the buyer to check for loose wires, components fallen off, and the little C4 boards for shorts. Then locate a local technician to try and fix it at my expense. Since the circuit is rather straight forward and the all manuals are included, any competent technician should be able to figure it out. It's even easier when they are monoblocks, one working unit should provide good reference to compare against. Worst come to worst, if nothing works out, I will have to refund his money and get back a broken amp. All the shipping expenses and 3% Paypal is kinda painful to swallow.

The buyer emailed me and said he already fixed the amps: $150 in parts + free labor. I will have to reimburse the buyer to make him happy with this transaction. I sold the Paraglows with Cobalt transformers, standard transformers, and AVVT 2A3 meshplates for $1325 shipped, net only $1286 after 3% Paypal. I spent $35 on shipping and now $150 for repair, so my net now total $1101. I should have kept the amps!
Link to my Paraglows photos:
http://photos.yahoo.com/bc/pt999/lst?.dir=/Paraglows+2A3&.view=t

Reply email from buyer:
"Thanks for taking the time to look into this problem. Your advice to
contact a competent technician was good. I have been working with electronics for the past 20+ years first teaching and for the past ten years I have been repairing medical lasers.

I was very careful to install the 2A3 tubes with the large cathode pins in the proper holes. After taking the time to examine the amps, I found several problems. On one amp, the 2A3 cathode resistor was open causing excessive voltage across the bypass cap causing it to breakdown. This was the cause of the popping noises.

On the other amp, this same resistor was a high value, 7K versus a
nominal 3K.

I have repaired them both at a cost of about $150 in parts. I used some premium parts but do not feel this is inappropriate. This does not count the cost of my time. I spent the better part of a day repairing them. I do not think it would be possible to get them repaired at this price from a repair shop.

Given what I know about electronics and the condition of these amps, I find it hard to believe that both of these amps were in good condition when they left you. However, I am willing to give you the benefit of the doubt provided you cover my costs for parts. I will throw in the cost of my labor at no charge. You can send it back via Paypal if you wish."

After thinking about the situation for a day, I finally emailed my buyer offering to pay for the standard parts replacements costs or a refund if he sends the amps back to me in its original conditions. Attached is my email reply:

"I'm glad to find out that you are the competent technician for the repair job.

From what I understand, on one amp a resistor is open, on the other, the resistor was of wrong value. So the fix is to solder the open resistor on one amp and replace the wrong value resistor in the other. I can understand that the shipping process can cause a soldier joint to come loose causing the popping noise. I bought these amps preassembled, the wrong resistor can only happened at two places, either Doc B. put the wrong value in the kit when he shipped it out, or the previous technicians error in assembly.

As for the parts upgrade, I find that it is not fair to ask me to pay for the upgrades in place of the originals. It is fair to pay for the standard parts replacements as Doc B. would have included in his kit.

Used equipments are sold as is, that's why they are advertised as used, and the buyers save money buying them used, at the risks of no long term warranty or support. I do my best to describe my used equipment and provide the buyers with plenty of photos to describe its conditions as well as packaging. During my 2 years of using the Paraglows, I have not noticed obvious popping noises or any other side effects. If you think these amps are not in good conditions when I sold them to you, you can packed them up and send them back to me tomorrow in its original conditions for a refund."
PT