You may want to research “Elements of a contract”. It is basic business law and has been established for hundreds of years and courts are still litigating it every day. It may save you from peering out from the wrong side of some bars someday. It is not my idea, it is the basics of business.
“”They should have (and I suspect most do) signage indicating that all sales are subject to verification by receipt on exit. “”
You are making stuff up on the fly. There wouldn’t be much point to this thread if all the stores had legal postings instructing shoppers that they would be searched after completing purchases.
Most of the legal issues have already been covered on this thread, if you have some legal information to post do it, don’t vaguely claim it exists, and send us off to scour the law books for it.