I think Cg trader system is best for authors. On turbo squid you get only 40% non exclusive, and on 3d ocean just 33%. 3D ocean is may best seller but, you can put your price, and they put price that is 50% to 1000% lower then prices on turbosquid and cg trader, so you have model selling for $3 on 3docean and 25$ on other marketplaces.
This is because they have some relay stupid licenses. One purchase of model is one use. Everybody will buy and use more then one time.
So tell me what will you rather have 1$ or 20$ for same model.
If you are annoy by credit you need to purchase every time when you sell, buy more credits (something like 100). This will be enough for 20 sells if is price of your model is less then 50$
Also I need to warn you if you go exclusive on turbosquid think twice. Any model you put on checkmate certification, you can't delete them from turbosquid for few years, and you are not allowed to sell this models on other marketplaces