[nineplay]

I'm not a flat-earther, but I'll daresay you couldn't prove that everyone who claims to have proof of a round earth is lying or deceived.

It's like some (alleged) variations of the young-earth creationist theory which posits that all the fossil evidence was deliberately planted by Satan to trick the gullible and only the true-believers can see though it. That's a pretty hard one to disprove.