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... 
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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When buying used over the internet there are no fail safe ways to guarantee that you won't ever get scammed.  The risk comes with the territory.  Use caution and common sense.
Did your buddy happen to deal with a Audiogon member or someone from another site?
It may be off-base to blame the seller 
given the sudden and catastrophic failure of the gear, it may be a crap build equipment issue.

i had three (3) sudden .... And mean unforcasted and SUDDEN .... Catastrophic failures on the $4k top-of-line AVR and blu-Ray player.
with the receiver , it was fine and next use two days later .... Kaboom! New motherboard replacement and gone for 5 weeks 
warranty coverage ... Okay....but. Something amiss. 11months later was an instant repeat. Good thing it had a three yr warranty 

the Bluray player ( a $1500 unit) crapped out catastrophically suddenly in mid-movie . It was 27 months old and three months out warranty so I was SOL with repair costs exceeding its FMV.

I sold the AVR and replaced the BR with a quality build Euro unit...and Euro / USA quality build separates 

the moral of the tale:

- the  expensive and shown-to-be-unreliable Chi-fi gear I had was crap build POS gear ...full stop

- mfg OEM warranty through a distributor matters. Too many have only a 1 year .... Caveat emptor. Most used gear won't have it and the bargain price reflects that.

- your seller may have sold used gear on a proper belief that it was out-of-warranty but all good ON DELIVERY with no knowledge of any issues. The risk is entirely yours 

I think I read that oldstyles buddy's techie found "counterfeit" parts, which led directly to the failure, therefor whomever repaired the first time is the culprit. Also it was the sellers attitude that set him (her) off. The techie said it was lucky it lasted the 30 hours, which smells of deception on the sellers part, why else would he lay down "attitude"?
I suppose the "recourse" is to buy new with warranty from a reputable dealer.
 Let the truth be stated. I think that audiogon, indirectly, plays a role in the loss of security rather then gains in security. In the old days, you could call a seller and talk to them about their gear. For me that was the best vetting one could do.  I always felt that I could gain an intuitive sense of the integrity of the seller based on discussion of their gear and their passion for the hobby. We can no longer do that. I feel that we are at a great loss in terms of security when these transactions may amount to many thousands of dollars of risk. I understand that audiogon is protecting its bottom line, but there must be someway to allow a phone conversation before a deal is finalized, or to allow reversal of a deal if subsequent phone conversations  are unsatisfactory. Audiogon… Put on your thinking caps and come up with something. Do the right thing!
Not entirely true about contacting before payment is made.
Basic Listing: 
  • All communication regarding the negotiation and sale transaction must take place onsite.  You may not provide any type of contact information until after an offer has been accepted.

Premium Listing:
  • Include your contact information

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.