I agree that it's about the quality and those that have been quality referrals will bring you more stable income by the way they're gambling. It's a niche that everyone should think of if they're for referrals and affiliate marketing.
The more quality they are, the more money you'll get as a commission from referring them and it's not going to be easy, there must be something you should do to take them and that's why too many helpful articles are there with attached referral links on some particular words.
This is why the casino thought it wise to have implemented this system that you earn from the activities of your referees, this has set the difference in the whole gaming industry and their affiliate marketing policy.