This is a question often asked by slots players after going a long time without winning. Online slots always spin randomly, but the RTP percentage is programmed into the game to determine how often winning spins come and how much players win when they do. That makes slots different from other casino games. It’s incorrect, then, to say that the casino controls slot payouts on any specific machine or spin. But the casino does choose the games and knows what the payouts are for those games.
Licensed and regulated casinos must undergo audits by regulators to ensure all of their games are fair and operate as advertised. That means even if a casino could control the RTP percentage of a particular slot (which it cannot), it would not be able to change it without regulators’ approval. Nor could it change the payouts without informing players.
All of which is to say, if you are playing at a legal online casino that has been licensed properly and follows the regulations of its jurisdiction, you need not worry about online casinos arbitrarily controlling the payouts of the games you play.