Have you ever worked on, or in support of an assembly line?
What you're describing sounds pretty typical of that environment, so pretty much what I'd expect in a fast food kitchen, which is usually just a simple assembly line.
My comments only apply to the kitchen, Costco here is known for paying pretty decently, especially by retail standards.
That said, there are staff at the exits who check receipts. They're less physically secure around the cash area because of size limitations resulting from them carrying lots of physically large items, so I understand why they check receipts more than other stores.
If they didn't it would be relatively easy to get out with a big ticket item without paying, all you'd need to do is walk out like a legitimate customer while all the eyeballs are busy.
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The Party told you to reject the evidence of your eyes and ears. It was their final, most essential command.
If you're not careful, the newspapers will have you hating the people who are being oppressed, and loving the people who are doing the oppressing. —Malcolm X
Real power is achieved when the ruling class controls the material essentials of life, granting and withholding them from the masses as if they were privileges.—George Orwell