Had one try to convince me irl once. He was adamant that I was wrong about it being rounding and demanded to know how I could be sure. I explained that I have sailed around it twice and never fell off and he didn't have much more to say...
Discussion
Most flat earthers have scarcely traveled more than 50 mile from their home.
If they had even an ounce of curiosity or adventurism, they would try to find the edge