Need Advice on Amp Audition at a Dealers

Verify with the dealer that they are OK with that. They might not be to protect their assets in case something is wrong with the amp. 

If they are local an in home demo would be best as always. 

I think bringing a "comedy stunt" amp that sparks and smokes a little would be hilarious.

Agree you must ask first about bringing any of your own gear!It would be good if they already have your speaker type and model as demo units, but not a deal breaker. And if they say no you just have to understand it IS a big deal. (what if something breaks. Who pays? YOU?)
Best thing is to bring music you know really really well. Make sure they know you are bringing music to listen to.(Sometimes dealers only stream...)
(for wolf_garcia.. At this point you are suddenly banned from 34,294 Audio salons in 26 countries. And you wonder... Why???)

Home audition is the ONLY way to do this effectively. We are dealing with SYSTEMS and theirs is NOT YOURS. Can’t be done? They won’t allow this? Then take your chances and listen to an amp IN THEIR SYSTEM. But you won’t be listening to an amp, will you?

Home demo or audition would be best. That way you get to listen to the new amp vs the one you have now in your own setup, system and room environment using your own cables, front end source components and your own speakers.