It is to stop items from accidentally getting charged to the wrong person. It benefits both people. I never expect a thank you for doing it. If something gets charged to the wrong person, everyone gets screwed. You, the cashier, and this idiot. Now everyone has to wait for the cashier to void the transaction and call a manager over. Congratulations, you played yourself.

I’m just gonna keep what I paid for, thank you very much.

Congratulations, you’ve now only played yourself here, ending up buying something you didn’t want or need.

You’ve also played the other person that is now missing an item