I know one way they cheat. They make fake articles and they promote them on facebook and google. In the article, the guy says that he has been using martingale strategy and that he has won a lot of money playing online roulette. And he posts proofs.....and he explains how the odds for martingale are good, that no one can lose 10 times in a row so that playing online roulette is a sure thing. Of course, he doesn't mention the table limits, so after some time you lose everything no matter how much money you have. In the end, everyone except casino loses.