You talk about 400 miles in 3 weeks likes it's from here to the sun nonstop! That's not even two tanks of gas, man. Cars are supposed to go thousands of miles! If you sell a car that breaks down in 400 miles, you don't feel any responsibility at all for anything else you might have said, just because you wrote the magic phrase "as is" onto the bill of sale?
Yes, perhaps they did something that caused the problem. But doesn't common sense suggest it was more likely it was something just waiting to happen? Other than maybe your own representation that you would never do such a thing, how do we know you didn't already know or suspect there was a problem that you just didn't disclose? (After all, you think it's fair to question the honesty of your buyer, so why not you?) Anyway, if you think it was abuse, you don't think there might be a way to show that? For example, if you
had gotten it inspected by your own mechanic
before and then inspected again by him
after he could be your witness that it wasn't your fault. (Similarly with a radio, not a car, perhaps you could have another ham verify the operation before you sold it and photograph it inside and out to document the condition.)
In answer to your question, yes, if I sold something that broke in 3 weeks, I would definitely do something and that might well be a full refund or at minimum a large chunk of the repair. (If you go to my
business website, you'll notice I give a 90-day
unconditional satisfaction guarantee on the software I sell, meaning they can get a full refund for any reason or even for no reason.)
As far as which of us people might want to trade with, well, let's see: I think I should take some responsibility for whatever I sell and you don't. What do
you think people will decide about that?
Finally, on the question of which of us is crazy, I put it to you: At least I apparently have a judge that agrees with me and you have, well, nothing.