He might get doubts after a while of you milking him, and you can cut and run then if you like, or you can double down. Throw him a convincer, something that makes him think you can really do what you say. Sure, it might cost you, but think of it as an investment in keeping the mark happy, and a happy mark is a generous mark so the return on that investment is almost as good as the one you promise your marks.
No con can go on forever. There’ll come a day of reckoning when your mark is going to expect to get what you’ve been promising him, and that’s when all your skills need to come out to play. You need to persuade him that everything’s gone wrong, forces outside your control have intervened and you can’t get him what he wants. The heat’s on you, you tell him, so you’ve got to flee but you promise he’ll hear from you again when it’s settled down. Before you go, remind him how many rules you and he have broken to get this far, just to stop him going to the police if he susses out that he’s been conned. But don’t worry, most of them don’t ever work it out, and you’re free to do what you want with their money now.
That’s all taken from Hustle, but it’s also what David Cameron and the Conservative Party did to Michael Ashcroft. They found their mark, reeled him in, promised him the power and influence he craved, chucked in a couple of convincers (‘Do you want to be Party Treasurer? It’s such an important role.’) but then when push came to shove and the election had been won, it was ‘sorry, I’d love to put you in the Cabinet, but Clegg’s blocked it’.
The only problem is that the Prime Minister can’t close up the shop, throw away all the phones and disappear to a nice hot beach until it’s safe to show your face again. And when you and other teams of grifters have pulled the same con on multiple occasions to the extent that actually giving the mark his prize is almost accepted practice, there’s no way you can stop him telling everyone what you did.
Con men are lucky creatures, though. Sure, you’ll face pig jokes wherever you go for the rest of your life, but maybe that’s better than being remembered as the con man who actually managed to sell democracy to the highest bidder.