Probably a boring answer but I know my grandmother's credit card information. I live with and help take care of her, so she doesn't mind sharing it with me. Not like I'm planning to do anything nefarious, but I guess technically it could ruin her financially.
That was my opinion as well.
She said that she didn't think it would be a regular thing, and by the time she realized we were good enough together sexually to keep at it, she just forgot to mention it for a while.
Which, I could see that being a realistic occurrence. We didn't exactly talk much when we would meet up.