Most flat earth claims are based on lies & deceptions - the remaining few are simply them not understanding basic geometry.

I address most of the common "Flat Earth" claims on my blog:

https://flatearthinsanity.blogspot.com/

Ask them if the Holocaust really killed 6 million Jewish people (and millions of others) or not. Ask them about 9/11. Ask them in plane contrails are chemtrails. Ask them if any actual children died at Sandy Hook. You'll find they swallow almost every conspiracy theory.

Now ask them what the centrifugal force would be at the equator. Ask how the angle of Polaris over the horizon gives you your latitude. They cannot do it b/c they are NOT actual experts.