It's really a judgement of character.
Yes, facts and product knowledge are important, but what sets anyone apart--be they an LBS, boy/girl friend, butcher, baker, or candlestick maker--is their character.
So listen less to what they say and more to the way it's said. That reveals their underlying character.
Personally, I'd rather deal with someone who sometimes says, "Jeeze, I'm not sure. Lemme check." than with a pompous know-it-all--who doesn't.