Beneath the bland veneer of supermarket automation lurks an ugly truth: There’s a lot of shoplifting going on in the self-scanning checkout lane. But don’t call it shoplifting. The guys in loss prevention prefer “external shrinkage.” Self-checkout theft has become so widespread that a whole lingo has sprung up to describe its tactics. Ringing up a T-bone ($13.99/lb) with a code for a cheap ($0.49/lb) variety of produce is “the banana trick.” If a can of Illy espresso leaves the conveyor belt without being scanned, that’s called “the pass around.” “The switcheroo” is more labor-intensive: Peel the sticker off something...