Great amp, crashed and burned after 30 hours... Buyer protection?

Fairly new at this hobby, but worried about getting burned by not so  honest sellers. How does one ensure the seller is a "good person" and will accept responsibility for their sale? Not have the attitude that "it worked when I had it" too bad it doesn't work after a few hours...!!
I have a really good buddy that has been doing this for years and he was severely screwed by what looked to be a very good seller. What is  your recourse? Need some good ideas before I dive in??!!
Thank you all 
Yes, tough luck. He could try taking that person to the court, but the case would be hard to win, I guess. However, it appears that the seller didn't disclose the history of the unit, so there might be a chance.
But perhaps having the unit repaired would be a better course of action.
How do you recognize good people to deal with? Go with your intuition, slightest hesitation - don't buy, especially expensive things. Still, intuition will fail from time to time, there will be losses. So what? The important thing is not to lose too much.  When buying records off ebay I throw away probably one out of five, that's accceptable loss for me.
I've had many transactions here and they have all, fortunately,  worked out well.  However, I do my best to vet the seller and purchase in a manner that helps protect me but understand that there is always some degree of risk when purchasing from a private seller rather then new from a dealer.  Just the nature of the type of transaction that is taking place.  At this point, even if I was burned once, I still would be way better off in terms of overall savings and the quality of the system I have been able to assemble due to these significant savings, not to mention trying a range of components.
Sorry, Just take the cover off. If my buddy had taken off the cover when he first bought the amp, he would have seen the some of the work and known right away it had been tampered with... your nervous?! Imagine me with the horror story to go further in the hobby!!
I think at the end of the day, my buddy was really choked with the sellers attitude.... because up to than he was very happy with every deal, on all the websites... one rotten apple in the barrel I suppose.. what we call the "A-hole" factor in my businesses... (will that be edited out?)
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