Just a guess but maybe denying at time of purchase costs them more than it's worth. Lots of go-backs from a cart full of stuff, and some of it is perishable and

Just a guess but maybe denying at time of purchase costs them more than it's worth. Lots of go-backs from a cart full of stuff, and some of it is perishable and you don't know how long it's been in the cart, so more shrink. Cheaper just to deny at the entrance.