Personally, I would send them to reputable casinos which aren’t as well known as others, just to be sure they haven’t signed up under another aff’s id already.
Phoenicians is one, Cool Cat Casino is another. Cool Cat is a new RTG, and is showing some decent conversions.
Phoenicians has multiplayer poker.
There are many more, but I don’t wanna have to think that hard right now. :p
Good luck!