I did a bit of research into this and found quite a few differing opinions and things that could be contested litigouslly. If you are in a store that does not make you sign an agreement or become a "member" to shop there, once you buy the item it is technically your personal property, and you don't have to show the receipt to anyone, no matter how nice they ask or whether they claim its a store policy or not. Of course they could always then say that you aren't allowed to shop at your store anymore, but I believe legally they have no right to force you to stop and show your receipt. I personally do it at places like Frys, but that's because I love frys and I'm a big computer nerd and would hate to not be able to shop there.
They couldn't physically stop you from leaving the store, and if they do so, they could be at risk for some legal trouble. I'm not a lawyer, but I've heard differing things kine about property rights laws and the requirements some stores do.
If you shop at places like Costco or Sam's cult, then yeah you signed an agreements saying they can search your shit and there's nothing you can really do about it. I personally think it's bullshit, and having used to work retail for way too long, they don't even really check the cart if you have lots of shit or anything that isn't expensive.
When I worked retail, I'd always just walk out after I bought lunch without showing them anything. A few of the door people were cool with it because they knew me and knew I wouldn't steal anything anyway, but a few door ladies got it up their ass that they were the "gatekeeper" or some shit. They'd get furious that I wouldn't stop and let them practically pat me down before leaving, but after a while they stopped doing anything about it.
Tldr, I believe you're not technically required to show your receipt at the door of a place that you haven't signed any "agreement" or contract with. However, they also have the right to tell you to never shop there again, and you'd likely have to go through the ordeal of making a big scene about it. I personally believe the urden if proof is on the store to catch me stealing something through means of loss prevention, not door greeter receipt checking. You don't technically have the right to dig your dirty little paws through my shit, so fuck off.
I try to be a little nicer about it though (not much)
