Just a thought experiment, let's say the earth is flat, looks like many professionals would know, including
Pilots/ATC/sea captain
Land surveyor and civil engineers
Astronomers and Geologists, at least the one dealing with experimental data
Militaries, at least radar operator and artillery
Just these categories are already a lot of persons, I assume I miss a lot of others. So how many person does it make in total ? 10 % of the population ?
Is that the one where they use the lighted poles at night and a board with a hole in it to prove the earth is flat? In that one they seemed a bit baffled and said they'd need to do the experiment again. To their credit, when they ran it again with the same results, they said they'd need to reevaluate their beliefs.