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 
Where was it purchased?  If auction site, call them immediately, start a claim right now, make sure to call by phone, there is a record of all calls, also start an email reply/question with the seller, another thing that is saved by the company of the seller who sold it. eBay? Amazon? 30 hours, ide be very disappointed as well. 
I agree with arctikdeth suggestions.  You must immediately call the seller and request a full refund and you should return the unit.   How did you pay for the unit?  Credit card charges allow to file a compliant and get your charges refunded.  I think PayPal has a similar claim process.  Based on the amplifier problems you described, I would return the amplifier to the seller, request a full refund and not agree to any repairs.  

I only use PayPal when I make a purchase.  Also check feedback on the seller. I have made many purchases on here and Ebay and never had a problem!
Thank you.... my buddy was screwed because the 30 hour point was after 63 days.... no recourse with anybody, seller said it worked for him and worked for my buddy, so tough luck.... repair shop told my buddy that the repair done on the amp previously was lucky that it even lasted that long... real hack job, counterfeit parts... I will definitely double check anything I buy, and do what you have all suggested... seller basically told my buddy to get lost...