Just like any other online casino out there, they have the right to require some kind of verification if they smell something fishy going on with your account. I get it, it sucks that your $500 withdrawal got held up, but maybe they're just being extra cautious or maybe they've had issues with you in the past that made them raise an eyebrow or something, who knows. They never promised that every withdrawal would be super fast or easy, so it's within their rights to take a closer look.