The number one way to stop shoplifting is to look people in the eyes. Shoplifters want to be invisible.
A store where every shopper gets greeted and seen is a hard store to steal from, and it happens to be a good store to buy from. Same behavior, two payoffs.
For busy periods, give your crew a warning signal. Mine was two words: "Look up." When something felt wrong, too much commotion in one corner, a feeling you learn to trust after enough years on a floor, anyone could say it, and everybody looked up from their station and scanned the store.
I started this in my coffee house days when we added holiday ornaments and discovered one person was working us every time the line got long.
The signal doesn't accuse anybody. It just puts eyes everywhere at once, and that's usually enough.
Now the part most owners don't want to hear. A friend of mine ran shrinkage for JCPenney, and her most outrageous story was a woman who strapped a comforter to the inside of her thigh and tried to walk out.
Memorable, but not the real problem. Most shrink comes from within: employee theft, sloppy receiving, mishandled returns.
So check your trash before it goes out now and then. Yes, the trash, because merchandise that leaves in a garbage bag comes back after the shift ends.
Train your crew on proper receiving and returns, because an error at either door counts against you the same as theft. And take a physical inventory by category periodically and match it against your system.
When there's a discrepancy, the cause is usually incoming, returns, or the dumpster, in that order.
You can't fix shrink you refuse to measure, and your bottom line pays for the difference either way. And if your shrink is small, high-value goods, decide whether you should sell from behind a counter at all.