Evidence based ways to show someone that they are being scammed?

One infuriating thing about the human mind is the way people refuse to see that a con is a con. Often showing a victim of a con evidence that the con artist is lying makes them redouble their belief and stop listening to you. I have seen this firsthand and I have read enough to get the idea that this is a generic problem.

As evidence shows that evidence doesn't work, is there a good way to expose a con artist and make their victims stop believing them?

via International Skeptics Forum http://ift.tt/1VxPRsm