It’s a reasonable question since it would be so easy to program casino games to cheat you.
However, I would have to say that, yes, in my opinion most online casinos are fair. Regrettably for the industry there are some rogue casinos out there but there are some protections you can take. All casino games have a ‘house edge’ of course which merely the percentage of the casino profit from the player’s original bet. Casinos are a business after all and need to make a profit somehow. You can do something to reduce the house edge – like selecting games that usually have a lower house edge (like blackjack), improving your skill level through lots of practice on free games or choosing wise bets but the bottom line is that you're never going to eliminate the house edge altogether.
So why do I think online casinos are generally fair? Well, to being with there is the random number generator (RNG). One thing you can do to distinguish a rogue casino from a reputable, trustworthy casino is to inspect at the casino’s audit reports. All reputable online casinos will publish on their website their audit report. Auditing companies investigate and certify that an online casino’s RNG are fair and unprejudiced and that winning players are actually paid. Further, if an online casino is powered by one of the key platform providers such as Microgaming, Playtech, Cryptologic or Real Time Gaming, it’s a pretty strong indication that they are reliable. These software providers aren’t going to gamble their valuable reputation by partnering up with an online casinos that hasn’t been granted a licence from a respected gaming jurisdiction.
So if you choose from a reputable casino, I don’t you should worry about whether the games are fair or not.