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This is the billion dollar question. We will never see the in and out of the programming rng or the algorithm. Anyone who has written or been exsposed will have signed hefty no disclosure agreement.
Honestly if your not sure or don't trust a site why would you consider depositing. Good thing is I don't see how it would be easy to cheat individuals. Could be possible. I think the real question is is it cheating all of us. Who knows.
Fortunately most sites have free rolls. So play them get a feel and decide. My thing is if your constantly losing you have to decide am I unlucky or do I suck, or is the site rigged. If any is your answer then don't deposit.
Good luck