So, if they were reasonable and intelligent they would think there must be an end to the flat surface somewhere.
Wouldn’t that make a great documentary: The End of the World, Revealed.
Why not take your life savings, put together a film crew, travel to the edge of the world, and film the experience?
The shock the rest of us would feel finally knowing how we’d been deceived would ensure word of mouth publicity and then great profit.
Since they'd never find it, they'd just claim that some unnamed conspiracy was keeping them from finding it. They are that dumb.