My grandmother died 25 years ago, and I remember being with her at a store with self-checkouts (they had them now and then back then, the tech wasn't so different), and she kept refusing, and stayed in line for the live cashier.

Finally, after about the third request from the bubbly, smiley young woman, my grandma snapped, "I want a human to check me out! I'm trying to save your JOB, young lady!"

And the girl stopped smiling and left her alone.