Hello,
The fact that he gives in-store credit solves the problem for me.
Personally I would really value a good shop and a salesperson who could give me critical information, guide me in my purchases as well as offer second-hand deals. They meet people all day... clients, reps, technicians and quite often know things in and out.
If you are seriously considering to buy those 17k amps then why not spend several hundred dollars on something you something and then ask him if he would do a brief demo. If he sees that you are a genuine high-end client with the budget, he'd be stupid not to serve you.
A amp demo can be very brief or it may take one hour or more with different speakers, DACs and cables etc. With the previous shop I was dealing with, they would routinely loan me expensive items for multi-day demos and let me know when some great second hand item came into the shop.
If a shop spends considerable effort in giving me good advice and service I will do all my purchases there meaning I will even pay extra than going to the dealer of that product but use them as an intermediary. Good advice and extensive demos saved serious money for me by making proper purchases.
mk00