Martingale doesn't work. If it did, casinos would be bankrupt and Vegas would be a ghost town.
And yes, its true that Roulette dealers can make the ball land where they want a good % of the time. So if the dealer sees some asshole trying to Martingale his way to riches by betting black, you can bet your ass he will be trying to hit that red within the next few rolls, or at least try to hit 0 just to piss you off.
The games are rigged, not literally, but in the mathematical house edge. In the long run, Casinos are always +. You can win big of course, but it will be because some poor guy has lost probably x100 of what you won.
The only slightly EV+ way of playing Blackjack/Roulette I know is called Blackjack/casino bonus whoring. Where the online casinos which give you 100% deposit bonuses. If you play a mathematically perfect game, you can clear your bonus, and get the fuck out of the site and withdraw your shit. But even then, due to variance, you can also lose your roll trying to clear the bonus or even be up slightly.
There are also a LOT of shady online casinos out there so I would only stick to even attempting this on the reputable ones.
Cash game poker with little to no house rake is the only pure form of gambling which I think is skill. As the player's skill determines how much edge you have over the other players, just like casinos.
In poker, large field tournaments are lotteries, even tourney players will tell you that. But the skill you have determines how many tickets you hold.