For the most part, they seek out who they want. They email you and ask you if you want to join. If you don’t get an invite, then you can apply and they will want to see your sites and may ask questions.
Really, anyone can do business with who ever they want. The crucial point is, do they keep their contract once they have one. So far with bodog that’s a yes.
(Sadly, I have gotten so cautious that I have to use “so far”. The days of general trust are over.)