Where does a sellers responsibility stop?


I have a ethics question that I need some input about. I just sold my pre amp to a buyer who made a local pickup. The pre has always worked flawlessly. He demoed it and then we took it out of my system. I started to remove the top to take out the tubes and pack them as they were when I purchased the unit. He said not to bother and so we packed it in all the original boxes.
He called me 3 hours later and said that the pre amp doesn't turn on. I told him that it had never had a problem like that before but, he was welcome to return it. He seemed really miffed at me like I cheated him. Now the problem is, I will be refunding his money but, how will I know that he didn't drop or short out or whatever the unit ?
Did my responsibility stop once it left the door?
agaffer
Agaffer- Hats off to you for dealing with this difficult issue in a very responsible manner. I'd deal with you anytime. A creative and way cool solution.
Agaffer, the way you handled this touchy situation is admirable. I'd buy from you anytime, without hesitation.

Best regards,
Plato
Agaffer, you're a gentleman and a scholar; and there's not many of us left...you were a cut above. Nice to hear....
Agaffer- I think we are all curious as to what the outcome will be. Please post an update when the unit returns.
I think you really bent over backwards and did more than expected in this case.....which is great service!

As several others said, if buyer comes to your house and actually gets to audition gear before buying, then once unit is out the door the buyer is responsible for any future problems since he is providing "shipping" of gear to his house etc. I guess whether you do anything further is purely up to your good will.

This is different than packing/shipping gear a distance to buyer where "seller is responsible" to provide working gear to buyers home........which can put seller at disadvantage since you never know if buyer did something wrong when using gear initially, but this is risk of used market.

Again good job.