Is it true that the customer is always right? This is the philosophy punched into any cheerful behind-the-counter worker. I worked in a Health Food store for several years and my experience is that the customer is not always the one with all the great answers in life.
One day a lady entered the store wanting low carb wheat flour. (Just that tells you how much she knew....) Her first line was something like this: "You probably don't know about this!" But that was not all. She continued to tell me that I most likely did not know anything, in between being shown all the low carb items we had in the store. After hearing for the umpteenth time that she could tell on my face that I knew nothing, I told her enough is enough, upon which she immediately stopped accusing me of ignorance and bought a bag full of things I had shown her.
Patience is a virtue! But the truth shall set you free! Sometimes the lady behind the counter is the one who is right.