PokerStars real money is 100% legit. PokerStars has been an industry leader since its launch in 2001. You do not stay as the number one online poker site for more than two decades if you are not legitimate!
But here is the quick answer. PokerStars is not rigged. It just appears that way sometimes due to the incredible speed of online poker. Because online poker sites like PokerStars typically deal hands 3 times faster than a live poker game, you should expect 3 times as many bad beats.