I know this is a really late response, but it did discourage me from ever wanting to sell again on head-fi and now I'm at a point in my life where I really need money, so I'm going to start selling my gear again.
When I sold him the amp, it was working fine, I tested it right before I shipped it, and it was fine. During the times he did try to contact me, I wasn't on head-fi and didn't know till later (I wasn't trying to ignore him). He didn't use the amp until maybe a week later after he got the amp (because he didn't have any cables), so maybe something happened, I'm not sure. I apologize though, and honestly think this trade was a fluke, he did get it fixed, and said it was a soldering problem. Anyways, I just want to say I'm not a dishonest person, and hopefully this never happens again. Hopefully, I will be able to rebuild a good reputation.