When I started playing in online casinos a few years ago, like most newcomers, I was pretty on my toes. A nice win wasn't paid out and all complaints and emails are useless, I've never seen the win.
You have to distinguish two things, really fraudulent online casinos and online casinos, which interpret the user rules very narrowly and collect the winnings at the slightest violation. Most casinos in the navigation are not actually fraudulent, but consistently look for violations of the user guidelines and problems with the minimum wagering amount.