As someone who has spent time putting together A/V systems in recent years, I have found dealing with many retailers akin to pulling out my fingernails with a pair of pliers!

When it comes to dealing with these people, I have one simple rule that everyone can use. If they start criticizing equipment they don't sell, IMMEDIATELY turn around and walk out the door!
It never occurs to this "pea-brained" salesperson that the customer he is trying to sell may own the equipment he is knocking so in essence, without knowing it, he is calling that customer an idiot for owning it!

This is the LAST type of individual who is going to provide the potential customer with knowledgeable advice.