What to do when buyer claims sellers item broken?


I recently sold a Bottlehead Paraglows amp with AVVT 2A3 meshplates on Audiogon. The tubes were triple boxed and shipped separately via USPS Priority insured. The amps bases were shipped separately via Fedex Ground insured. I was very careful with all my packaging. I know these amps work perfectly before I shipped them out. Now the buyer received the amp and the tubes, and claims the tubes glow up then died. This is the first time I have had problem with selling my equipment, and I am not sure what to do here. If the amps and tubes arrived without any visible box damage, how can they be broken? There are minimal circuits in the amps to be broken, especially inside a wood box covered by thick foams and double thickness box. Please understand that I am not saying my buyer is doing anything to it, I just need advice on what to do next to rectify the situation. I don't sell a lemon, and I don't want a negative feedback from any buyer, ever.
PT
pt999
Tubes amps can blow from connecting without a load (speakers) connected. File a claim with shipper. Ask buyer if a local tech can have a look. Shipper may have dropped unit. You have to get them fixed . Ask buyer if he shorted them or damaged them , see what his response is . Otherwise you have to take them back. I once sold a Revox int. amp to a gentleman. I sound checked it , he picked it up! Next day he says it only plays at very low volume! I had to see whats up so I went to this guys apartment in the furthest away from me downtown part of China Town in NYC . He had a new pair of B&W 802's so I thought wow maybe it blew or got a short. So I check it out and he had the -20 mute button depressed ! Another friend of mine got no sound from his new stereo system , until I released the magic (tape monitor) button . Good luck resolving this mess.
http://cgi.audiogon.com/cgi-bin/cl.pl?misctunr&1034968130&2&3&4&

This item is up for sale because of the EXACT same scenario. I suggested the buyer have it repaired locally and I would pay for the repairs needed, then I would chase the insurance claim. It's worth noting the item is in perfect cosmetic condition, the buyer claimed that there were gremlins in the tuner and insisted on returning the unit to me for a full refund. I refunded the money, ate all the cost, had the unit checked out thoroughly by the manufacturer. Was the buyer being honest with me? I suspect he thought he was. My integrity is worth more than a few hundred dollars.
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.
Did the new owner know how to properly install the 2A3's? If both amps failed upon power up, it would seem to me that they were not (properly installed) and it would not take very long (a few seconds, as described) to trash the amps.

If so, this should be easy to determine upon inspection by a tech.

Sorry I do not have a solution, but this is what I suspect may have happened (based on the new owner's description of the event).

I own the Paramours, by the way, and yes, there is not much to go wrong if they are properly used.
Man, what a tough situation. I agree with taking it back and filing an insurance claim. The last thing a good seller needs is negative feedback.
I recently sold a CDP I had for 5 months. The buyer informed me the balanced outs were distorted. My pre is only RCA's so I had no way to know of this situation. I immediately refunded his money via paypal and included money to ship it to the manufacturer. I will pay for the repair, have it shipped back to him, then he will pay me the original price. He was a good sport about it as he could have just sent it back to me and bought somebody elses.
Good Luck,
Patrick