I sometimes get them at work. I can't not answer, but sometimes I can work out what they're up to and get them off the line before their reflexes can catch up.

Other times I just tell them the literal truth.

- you do realize you're trying to steal from a charity?

- [mumble]

- we are a charity. You're trying to rip us off and hurt all the people we're trying to help. Which might include you or your family, some time. How do you feel about what you're doing?

They don't usually need more explanation than that.