I think it's not just that you need somebody really gullible - it's that you need somebody both gullible, and dead-set on not feeling like they've been fooled.

I think it's not just that you need somebody really gullible - it's that you need somebody both gullible, and dead-set on not feeling like they've been fooled. Extremely gullible, desperate, mentally ill people are more likely to stick, even when they get hints or straight assessments that it's a scam. At least, that was the impression I got from an old lady who lived near me, who managed to shout down a stream of people telling her that her 'secret agent boyfriend from plymouth' she was sending all her money to wasn't real. I think there's a bit of a parallel to cults like scientology - the more incrementally ridiculous you make the story, the higher the feeling of shame is when you have to own up to being fooled, making some people go in deeper rather than back out.