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 
oldstyle
After the offer is accepted and you talk to the seller, then get a bad feeling, it is too late, if you cancel... they will slam you for backing out of the deal... so that does not work... on a couple other sites, the USA and Canadian audio-marts, you can phone and email about the transaction before committing to your hearts content. The only thing the moderators do there, is turf out the scammers... and the community is quick to report the scam artists...  
..for me, it would all depend on how much money is involved and the amount of grief and time it would take to travel down any legal road.  If it were for a couple of hundred dollars, and after a brief try at making it right, I wouldn’t ruin my days left on earth with this.  Just move on.
Dill. What you write is correct but the buyer has no influence on whether the seller lists as premium, and few do. So for most transactions, no contact is allowed. I cannot overemphasize the value of contact by phone.