There is a long list of independent companies and regulators that certify the payout percentages of casinos, as well as ensuring that their gaming offerings are fair and legitimate. Two of the biggest testing organizations are eCOGRA (eCommerce and Online Gaming Regulation and Assurance) and TST (Technical Systems Testing). Additionally, most casinos and gaming manufacturers are more than happy to make their payout percentages public. NetEnt, for example, is a pokies developer who posts the RTP of every game they make, as well as a version that you can try for free, on their website.