Supposedly you have to play more to increase your chances to get one of the bigger prizes. But my own research currently points (with a relatively high degree of confidence) to the fact that the site might not be fair for the free rolls. The owner could implement the first change (from the 2 suggested by me above) to prove me wrong. The second change, with the JS auto-verifier can be implemented by anyone who knows JS coding and has some free time (the owner could do it too, of course).