The problem in saying site rigs rng to favor someone is that whom should it favor? If you run bad against regulars, what would the site gain with that rig?
In theory site would gain if they rigged games toi favor weaker (losing) players. I have witnessed this once, on a sit that forced run it twice and made so that the huge underdog won the second one almost always. Found out few posts in the internet about it where a former worker for that site confirmed it. Of course I don't know what was the truth, but to lose so many run it twices against 1 or 2 outers is VERY unprobable. Stopped playing there, and it wasn't any of the major sites with a major license.
I have run bad at GG network against everyone, and continued to run bad when depositing more. At least they didn't rig the games to my favor. 
GG is the most growing network at the moment, and they are making a lot of money. And the bigger they get, the more money they will make. It would be insanely stupid to rig rng, as it would be a huge risk for little benefits. Site makes money by rake, and the more games are running the more rake they collect. And it looks to me that games are running very well, so the benefit from rigged rng would be quite minimal.
Of course the stupidity and greediness of humans will always surprise us, but I don't think GG has rigged rng. They do have lot's of other scams/grey areas in their business model though.
And the bottom line is, if you think the game is rigged but you keep playing it, it's your own fault.