u/isshakes

I just agreed to buy a relatively new SQ-6 for $3k. The guy says it's barely used and in great shape and he seems cool but I don't know him and have no reason to trust that (especially at this great price). Per my understanding of A&H's warranty any remaining coverage won't transfer to me as a secondary buyer, so I need to make sure this thing is in good shape. I can't spend an hour testing this and depending on it's location I may be testing it out of my trunk (I have a 400W plug in which should run it fine, though I'm worried it may introduce some noise issues).

What are some red flags I need to be on the lookout for? And what tests can I run in 15-20 minutes to be reasonably confident it's in good shape before I pay him?