Bear in mind also that rakeback in itself is a very competitive aspect of this industry, and if a player is wanting rakeback, 9 times out of 10 he is wanting the best rate possible. Established sites are able to offer a higher percentage than a beginner could, as they’re usually generating 30k+ in MGR.
To be honest, I’d recommend against doing rakeback as it’s hard enough to break into the poker industry, let alone the rakeback part of it. It also requires a lot more administrative work IMO. I’m not anti-rakeback or anything, and one of my sites I have rakeback offered on it, but just think it’s an aspect of the industry you should stay away from when first starting out.