The linked article bases this on three sources; one former employee answering on Quora, one more answering on the consumerist, and a third answering on a 45 com

The linked article bases this on three sources; one former employee answering on Quora, one more answering on the consumerist, and a third answering on a 45 comment reddit thread not specifically on Costco. Take it with a huge grain of salt. I've actually worked at a Sam's Club and done checking briefly. I feel that this is the stated reason, but you're talking checking hundreds of receipts over a 4 + hour shift, often massive ones due to multiple flatbeds of groceries or goods; the idea its being used to check up on the cashiers is absurd to me. Many times, high-dollar items like meats you'd want to check are already in freezer bags, obscured from view. I think its mostly to prevent high value items from leaving, or at least to alert management they are. I mean, anyone who his rung up a vending machine route guy and his 100 boxes of candy who kind of scoff at the retiree checkers doing that fine of an job.