There are many, many, many examples of exactly that happening: they run experiments, the experiments prove them wrong, and they instantly declare the experiment to be wrong. You can easily find them on YouTube, IIRC a flat earth documentary on Netflix also features exactly this at the very end.

There are of course people like grifters in the community who don't believe their own words, but the believers won't reason themselves out of this position they didn't reason themselves into.