A great deal has been written about the honesty of land-based slot machines. A great article by Steve Bourie is titled, “Are Slot Machines Honest?” and originally appeared within the 1999 American Casino Guide. (It can be found quality online casino slot by searching for the title in Google or Yahoo!.) Physical, land-based slot machines have a great deal of “variations” (being polite) than can deceive the player. Of course, they can be all illegal and do not happen. But read the article, closely.
In contrast, online casino slots use an electronic “random number generator” or RNG, operating inside an extremely large computer program that manages the game graphics, the player accounts of individuals that join the game, the statistics of every hand played, plus much more. The random number generator is hard-coded software instructions that do not change. There's no “sense switch” (see the Bourie article) that can be flipped to give players worse odds. Regarding control parameters, each use of the RNG is the same as the final use, and also will be the same as the next use. The numbers will come out randomly, although the pattern of randomness never changes. This is a true benefit from software-based online casino slots.
Land-based slot machines could also have payout percentages as little as 83%, which is just not true with online casino slots. In online gaming, each machine has the same winning percentage as another machines. You may see the payout percentages for many online gaming sites, and you will see that it rarely drops below 95% - that is, the house makes a 5% profit, on the typical. The truth is, most casinos can document that their payout percentages are in the 97% - 98% range. This means you can spend an hour, gamble your $100 stake about 3 times, and on an average it will cost you $7.50. But players don't gamble to be average: the true reward is the well-paying win. And also the well-paying win is balanced, keep in mind, by a number of players who lose and finance that win.
So are online casino slots fair? Yes, they clearly are. The software that operates the games is tested regularly by independent testing laboratories (look for logos at the bottom of the casino website), and no game is individually controllable to be biased. That is a far cry from the specific situation with land-based slot machines, appropriately called “one-armed bandits”.
Players improve odds, they get absolute consistency across all games - but nobody can guarantee a win every time. That's just the nature of gambling, and that's involved in the thrill.