You can be smart and still be conned.
I know many smart people who have been conned by this type of personality. I have been conned by this type of personality. It's hard to recognize and admit. But once you do, you'll see the con in the future. Hopefully.
Personally, I think it best to not call them morons. If you are trying to convince them that they've been conned, questioning their intelligence at the start will close their ears. Very difficult to break the spell until the burned hand teaches. (I'm hoping for an instructional first-degree scalding, please.) Then bring bandages not blame.
(minor edits)