Random anecdote: Yesterday I accidentally stole two different things from self-checkouts. At the grocery store I stole 2 flats of Coke Zero because I forgot the stuff under the cart. At Home Depot I tried to buy 2 packs of leaf bags but somehow ended up with 3. I noticed the Coke problem after I had left the store but in time to go back pay for them, but not the leaf bags.
If the store had noticed the problem would they have treated me like a criminal? I'm the type of guy who goes back to pay for something even after a successful accidental theft, which I suspect puts me in the minority, but I don't think it's uncommon either.