So--innocent until proven guilty is no longer a thing?
If he paid for it then yes it’s his but you should provide the receipt if asked when leaving.
If it's his, then no one else has any right to ask him anything about it. It's his. Not the store's.
Bizarre thought process...
The local Home Depot has now locked up 90% of their power tools, lawn mowers, weed eaters etc because folks are just walking out of the stores with them. According to you just say it’s mine and you’re good to go.
Ever walk out a store with a bag or cart full and the buzzer goes off because a tag or something sets it off? What do you do.. run? I’m guessing you stop and someone checks the item or receipt or a cashier says your good.
Ever go to a Sam’s club or BJ’S and there’s a guy there checking your receipt and verifying it against what’s in your cart.. you just paid for it’s yours... they have no right?