Nope. Their mistake, their problem.
If they can't be trusted to not screw up handling people's account, then I would give them as little access as possible. What is not to say they will take more out than they are supposed to. Good luck getting THAT back.

That is not to say you can't give the money back. If they notify you, you can still give it back. I would not let them help themselves to correct their mistake.