Almondx, i also do the same as u when testing amps, cuz i wanna hear how the chords sustain or hold together. Also, wanna hear how the notes remain audible instead of being muddy.
I usually test the amp, play simple chords n fiddle around with the settings n eq, n hear wat difference it makes whether subtle or have a big range. Rather than set the amp to higher gain n solo all the way or play their favourite riff lol
I recently bought an amp from davis, and it was a short n sweet affair. They were v helpful, altho they were not like super smiley n frenly(Like they noe u super long alr), they didnt show any unwillingness to help, considering they had to set up the head to a cab, n there were quite alot of ppl coming in the shop.
I just hit some chords, tested the amp controls, n i bought the amp.... N janet even mentioned that it was fast, so they do allow u to test. Of course it best to do some home work first on wat u want to buy, then test it. It also better for you, cuz u dont wanna end up selling something u just bought shortly after.
In short, im happy with my purchase, n the service maybe not super friendly like old pals as one would expect, however was V PROFESSIONAL. They even helped to push the amp down to the carpark for me, and that wasnt even requested at all by me. So that was a sweet gesture (Cuz when i carry the amp home later, i probably did my quota for this year's fitness exercise)!!!