I'm suprised they even bother to try and stop it. My grandfather works at WalMart, and said that they're told to not try and stop shoplifting because they don't want customers to be afraid to shop there.
Who are you checking, the cashier or the buyer? My guess is a deterrent for some kind of collusion.
Same with Fry's. Not the same with Costco; there, you're subject to the membership agreements.
At Best Buy I stopped shopping there for years. I don’t remember why I eventually went in one again, but in the years since I’ve never been asked once. I do wish they’d get rid of the guy at the door entirely. It’s weird. And they always greet you from the side or back.