I never worked in a brick and mortar store but I wonder if they purposely only place 1 or 2 items onto a shelf to create a false sense of scarcity. Meanwhile they have a whole pallet of them in the back. As a customer you would never know but if it came down to taking legal action, it would probably be pretty hard to prove without a doubt this was done on purpose.
Scarcity or feeling like you're going to miss out on something (especially a deal) is a really powerful trigger. I generally ignore most advertising but man when you see that there's only 2 left of something you want on an online site, I would be lying if I said it didn't affect me. Luckily this tactic is less potent now for a number of things because so many online stores sell the same items.