I've had this a fair amount of times with guitars (and not guitars that are mega high end either).
I was at a snooty shop in York (my home town) and asked to try a Jackson Rhoads 5 (a mere £799). I'd been after one for a while, but never seen the ivory model in person.
I was a teen at the time, long hair, patched leather jacket etc, and asked the salesman, also a teen, long hair, little shirt with his name on a badge, if I could try it.
Conversation went something like:
"We only let people who are going to buy the guitar play it."
"Well I don't know how it plays."
"It's an expensive instrument, it plays great."
To be honest, I would have been fine to buy it and know that it was right because I'd tried the same model but different colour before. However, we all know that woods are different and who's to know if this one was a turkey?
I asked for the manager, put my money on the counter and pointed at it and asked him what it was. When he said "A lot of £20 notes *grin*" I responded with something like "Yes, a lot of £20 notes you aren't getting because of this twonk" and pointed out the salesman.
As it happens, I ended up buying an ESP M-II from Evil Bay.