I have long felt that the extreme gullibility of many religious people leaves them wide open to exploitation by fraudsters who pretend to share their faith. Well, today I found out that this kind of fraud is so widespread that it actually has a name: affinity fraud. A definition from wisegeek.com:
Affinity fraud refers to different scams perpetuated on a group of people who are specifically connected to each other by race, religious background, occupation, family, gender or age. The person or people perpetuating affinity fraud exploit these connections, and in using the commonalities of a particular group, create a scheme that will be most appealing to that group. The end goal of the criminal is to steal money from participants, and it's an unfortunate and frequent occurrence in many parts of the world.
The term is often used in relation to financial investments. A search on Google will reveal many sites giving more details (such as here and here). From these sites you might get the impression that it is a relatively new phenomenon but I suspect that affinity fraud must be as old as religion itself.