Do i legally have to show my recipt to the crypt-keeper posted at Wal-Mart's exit door?

If you did not know about the policy, you do not need to allow it. Refusal, however, will lead to the private property owner excluding you from the property so that further entry is tresping. I addition, if you are wrongfully detained and searched, your remedy is simply to recover your damages in a civil suit. As the usual judgment in such a claim is about $1.00, there is no point in doing it. Now that you know about the policy, however, your entry constitutes your consent and the private party can do anything with your consent