Not that this is any less odious, but....
"I had never seen a company who's normal business practice was to (basically) "frisk" it's customers as they were leaving the store."
Actually, there are quite a few companies that do this---but it's "nothing personal".
This is to prevent the scam where a cashier working with a "customer" doesn't ring up all that is "purchased"; the guy at the door is making sure your items match up with your receipt. It's not aimed so much at you as at their employees, and, yes, they should find better ways to keep them honest. I certainly avoid such stores as much as I can.