BJs, Costco, and Sam’s Club are membership stores that can be utilized only by members who purchase an annual membership and show said membership card to enter, and these stores are otherwise NOT OPEN TO THE GENERAL PUBLIC. ... period ...
There’s a laundry list of contractual “rules” members are required to follow to maintain their membership, and showing their card to enter and their receipt to exit are a couple of those rules ...
I've been a member of B.J.'s for over 40 years, and have never had to show my card upon entering. Of course you have to scan your card before you can check out, but they've always asked to see your receipt upon exiting.