There are some big stores that have a policy of having someone check a person's receipt when they leave the store to make sure that it matches with what they have in their bags.They do this in order to cut down on people stealing from the store. If I unknowingly have something in the bag that I didn't pay for, but when I went through this "security check" it wasn't noticed, do I have to return the item? My question is, does the fact that my bags were checked and this item wasn't noticed, make this into a case of ta'us akum in which case I would be allowed to keep it? Or does the fact that I put it into the bag (even accidently) make it into a ful-fledged act of stealing from a goy, and I would have to return it? An added point, is that even the checking of the bag might not make it into ta'us akum, since it often done in a perfunctory manner just to put some fear into customers but not to actually do a thorough check.