I beg your pardon! I can't see how anyone could possibly think other than it must have been faulty as sold! The fact that it only ran for 6 hours makes it even more probable. If this is your attitude to buying any second-hand item, can I let you know when I'm next selling a car? I promise that it will run until it gets to the end of the street.
I think that you are living in fantasy land, Steve67. See comments by Barrymagrec, just as for instance. This was a USED item, not brand new, out of the box.
I have no idea under what conditions the amp' was sold, but if "sold as seen", tough. If there was a 6 month warranty, or whatever, fine. To PROVE that anything was wrong when it was sold would, in all probability, be essentially impossible.
The example of the car is a very poor one - private sales have essentially no cover under law - that's why so very few people buy used cars privately, me included, just not worth the risk.
.................Nevertheless It is the responsibility of the vendor to either refund or repair the amplifier even though it was sold in good faith...................
As a blanket statement, I think that your are on VERY thin ice with that too, or worse.
If Mandryka is honest in his dealings and admits that it worked OK for 6 hours............... If it had gone pop when he plugged it in, THAT is totally different.
That said, I suspect that Emporium will be sympathetic in dealing with the hassle.