That's an interesting story. As I've explained to more than one Walmart who called because someone refused to show their receipt to the "receipt checker" at the exit, they can't 'make' someone stop and do that...unless they have sufficient reason to believe the person has stolen something. And then they'd better be damned sure before they detain someone otherwise they're looking at a civil lawsuit or even criminal charges for false imprisonment especially if the encounter leads to a physical altercation.
Right on @Rock Man I worked Loss Prevention at Kmart in college (remember the Big K???) and the one thing they drilled into us over and over was NEVER detain/stop someone unless you were 100% sure they had selected the item and passed every possible chance to pay for it and were leaving the store. Civil liability fears far outweighed any concern for lost profits.

