Reputable online casinos are not rigged. Period. They have software providers that put a lot of effort into insuring fair game play, insuring the RNG is both secure and sufficiently random, and actively audit their licencees to prevent tampering (inside and outside).
Casino games are EV+ for the house, they make too much money over time for the house to remotely risk their reputation by screwing with software. That's not to say that even a very large casino operation cannot lose a lot of money in a given day -- they do -- the variance is significant.
People play a few hands, a few hundred hands, a few thousand hands, and claim it rigged. LOL. You'd have to play a few hundred thousand hands to millions of hands just to reduce the variance enough to know whether the actual return approaches the expected return. People that claim rigged just have no background in mathematics and probability.
Olympic (The Greek) Casino is legit.