Why does it matter? If the shop is good and you are getting your moneys worth whether this guy is "racking it up" or not is none of your business.

It is his business to know what he can charge for a product. Some time just ask him if he knows what so and so charges for some thing. Let him answer without setting him straight, if need be. He'll get the idea. If it's worth it, pay it, if not, go some where else and wait for the "Going out of Business sale".