Basically what they do is build themselves up through something like a social capital pyramid scheme. This eventually collapses when there are no greater fools and when all their promises fail, but the good ones already have the next grift in progress before the first one collapses.
Trump is truly one of the greats at this. Not only does he do this very well but he builds the next grift off the previous one. He's IMHO the world's premier expert in "failing up."