Bring in a CD or record you’re very familiar with so you can readily identify any differences in playback. Bring in a particularly well recorded CD to see how well the equipment deals with that in comparison to your current equipment, and bring in a particularly poorly recorded CD to see how much more the "poorness" is exposed. I tried this with some telling results on my last speakers purchase. Find out if the equipment being auditioned is broken in or not. No sense in the dealer providing the listening material. You know they'll cherry pick extraordinary material. I did ask them at the end of each listening session to play the best recording they had just to see what the speakers were capable of . That was interesting too.
Mike