Andrew are you hanging out a lot these days with Alan? You sound more and more like him everyday.
Look nobody is required to prove anything about income or even winnings, just like we don't require anyone in the private sector to prove what they make. All that is necessary is 1) that if a person is claiming winnings anything at all (longterm) that the math support that, meaning they are doing something that makes it a longterm winner and 2) that the numbers add up.
If someone is claiming to make 5 million a year playing red chip level blackjack, that is a case of the numbers not adding up. We don't really get a lot of that, but we do get a lot of #1, where claims of any longterm winning aren't supported by math. We get these claims where someone is depending on "special plays" or gut feelings or rabbits feat, maybe cloves of garlic around their neck to overcome -EV on a long-term basis and I am sorry but that is nonsense. The very low bar is have the freaking math work.