You will read reviews of this film saying its predictable and badly acted, especially concerning Lindley Crouse as Margaret Ford.
I don't think most reviewers actually get the plot. It's more complicated than you think. There comes a point, quite early in the film when you think you've sussed the con, but you haven't.
Watch it again, and again if necessary, there's a con within a con.
I think people like to give themselves too much credit for figuring this film out, then right it off too quickly, it gives them a self gratifying sense of superiority.
If you think you got it, you probably didn't.