Those Tricky Gas-Sucking Pumps

Conversation I had with a relative on my recent trip back home:

AUNT: The strangest thing just happened at the gas station. When I filled up my car I left there with less gas than I had when I got there.

ME: Oh?

AUNT: Yeah, it's like it sucked the gas out of my car instead of putting it in. Is that possible?

ME: Well...

AUNT: So then I went to another gas station and it put the gas back in.

ME: ...

AUNT: I think I know what happened. At the first gas station when I put my card in I pushed debit instead of credit.

ME: Uh...

AUNT: At the second gas station I pushed credit and it worked fine.

ME: ...