When I lived on the Upper West Side (Manhattan) in a roach-ridden rent control apartment that I still remember fondly (all but the mouse) ... I used to get mailings from such a preacher.
The mailer was titled "God's Gold Book Plan." It promised that if I would send them money I would win lotto or have some other piece of luck.
It was funny and sad, all at once. They were scammers preying on the many poor people where I lived; but in a weird way they were also selling hope, and I would imagine that some people sent them money they could not easily spare. Hope is precious, and life can be very, very tough.