Lucky, you are probably FAR better qualified to demo the keyboard yourself than 99% of most salesman. For starters, you are pretty familiar with how to PLAY an arranger - many salesmen, if players at all, are probably live band musicians, and as we all know, playing an arranger is quite different to normal playing.

And really, c'mon... all you have to do is pick a style, pick a RH sound, and hit PLAY! How hard can that be?! Finding out how it sounds in YOUR hands is probably better than listening to some salesman who probably knows little about arrangers, if anything at all, and a better situation to judge whether you want it or not. Either the salesman is a GREAT player, and you'll be disappointed when you get it home, or he's a terrible player, and will make it sound awful! In which case, you won't take it home...

Trust your own judgment and experience, and make sure the store has a good return policy, and make yourself aware of any restocking fees if you choose to return it. Then come here for answers. Best knowledge base about arrangers on the planet...