No. Online poker players frequently express this worry, but it is largely false. Although there have been a few instances of poker sites defrauding their users, these are quite uncommon, and it is getting harder for a site to get away with it. In any event, if you play at trusted sites, you shouldn't worry about anything. Fixing the games is not advantageous to the website in any way because they don't care who wins. Every time a player pays rake, they get paid.