If a sign is clearly posted stating the fact that a receipt will be required to exit the store with any merchandise, case closed.

Just as with whenever something is sold "as-is", as long as it states that anywhere within the contract...seller is relieved of any return obligations. Look it up.

Think about it, you are telling a customer that that toaster will cost $20. If you give the store a $20 bill, they will give you a toaster. That is the agreement you made. You agree that swiping your credit card and scribbling your signature will be a fair trade for that toaster. If you try to break that rule, you agree to being arrested.

This receipt stuff is common sense. It sucks, but that's what happens in a system of checks and balances when society's bad apples spoiled the bunch.