Having a little bit of knowledge ..
I'm not the most knowledgable guy when it comes to audio but I've learned a few things. Having some audio knowledge gives you confidence as a shopper that very few of us have in other areas in our life. Armed with a little knowledge the salesman is not going to blow smoke up your *%!. For example: when they try to sell you expensive speaker wire, ( I know its snake oil ), so I tell them I need 180' and can't afford it at this time.
Or a high school student offers you some sales help. You ask "does this receiver drive a low impedance load?" Its fun to watch as they become baffled and go for help. And if your girlfriend is with you this will impress her as she will think your not the dumb smuck she thought you were.
Having more knowledge about a product than the dealer, you can ask some really tough questions or play the novice and listen to all the BS, Its your choice. :)