I would have spoken to them after their conversation when he was wondering around or after he left the store. It's the guy's business. He can tell people whatever he wants.

I am a computer guy. You don't know how many times I walk around CompUSA or some other chain store and hear the employees giving horrible advice. I kinda grit my teeth and bear it or if the person is totally clueless, I wait until the salesman walks away and give my opinion.