[AppyPappy]

refusal to show a receipt does not constitute reasonable grounds for detainment

That depends on whether or not you are on private propery. They have a lot of latitude when you are on their property. The best idea is to stay off their property if they engage in this behavior. But I suspect most offended people are powerless to do that because they are sheeple.

[Quick1]

That depends on whether or not you are on private propery.

No, it doesn't. The grounds for your detainment must happen BEFORE the inquiry of the detainee. The store retains the right to ask him to leave their property, however.

The best idea is to stay off their property if they engage in this behavior.

A good idea, but most stores don't exactly advertise the fact that they check receipts. I like the idea people have had to immediately walk to the return counter when asked to show a receipt.

[ShadowAce]

That depends on whether or not you are on private propery.

Are commercial stores private property, though? In several instances they are treated as being public property--ADA enforcement comes to mind. Right of entrance comes to mind (With certain specific exemptions). Discrimination laws also apply.

However, they are owned by private individuals or companies. I'm not sure what their status legally is--does it change from instance to instance?