Can we just take a moment to consider how LONG it took Dear Jim to plan The Great Game?
Painting an oil painting takes time. Imitating a master -- in such a way to successfully complete a forged painting -- takes time too. A considerable amount. The little old man mentioned in the show had to adjust his style to properly imitate what he meant to paint. He'd make some sample paintings. It wouldn't be something that took a few days.
Doing a successful forgery is complicated. For the purposes of the show, they did some handwaving over how experts would be testing a painting, researching it, comparing it to past paintings, etc.
(Okay, let's be honest, they did a LOT of handwaves. Realistically any specialist would have looked at the artist, his life, and what he was reputed to paint, and they'd've known long before SH that it was a fake.)
Let alone the other things, like the bribes. Sure, Jim probably invested a lot of bribes. He couldn't bribe everyone. But he could bribe enough people for a short-term scam to work out. Sort of.
