For online slots regulated by gaming commissions, the results are linked to a central system that tracks the game's payout and win rate. This ensures that the reported Return to Player (RTP) percentages are accurate. Other online slots are regularly checked and audited by licensing boards to ensure fairness.
Internet casino gaming remains illegal in every state that doesn't explicitly legalize the games. A player using an unregulated gambling site in any state but New Jersey, Nevada, Delaware, Pennsylvania (and soon West Virginia) is technically breaking federal law.