All the strategies described so far are based on a well-functioning roulette wheel with balanced probabilities. Playing on it is gambling, and you only win if you are lucky. You can be lucky even before placing your bets, and you can find a roulette on which it pays to bet on (meaning that you reach a statistical return to player of over 100%). Whether or where you succeed in finding such conditions is never guaranteed.
Betting after spinning the ball
Some casinos allow betting even after a ball has been played. Even a very small rise in the probability of hitting a certain number can tilt the statistics in your favour. Thus, if you can somehow reliably calculate approximately where will the ball hit, your chances of winning increase significantly. In real casinos, your only hope is an autistic friend who can estimate where the ball will land in a few seconds. In online casinos, you can try automatically reading the motion of the ball and the position of the numeric wheel from a video stream in order to calculate where will it hit using a physical model. We tried to develop something like this once in college, but were not able to complete it. In any case, we are not quite sure if it would ever work. It certainly wouldn’t be easy!
Defective roulette (or dealer)
I once heard a story from a trusted source about a man, knowledgeable about gambling, on holiday somewhere in Africa. Of course, in Africa many things do not work quite as they should. One of those things was a newly opened casino near the hotel the man was staying at. An occasional gambler, he went to play there. He noticed at a roulette table a newly trained dealer, throwing the ball with an identical strength and direction in every play, always giving the ball the same spin and starting from the same number. In essence, her movements were so deterministic that the ball was hitting the same third of the wheel every time. He won a five-digit sum in dollars, four evenings in a row, forcing the casino to close after each big win for the rest of the evening due to its payout limit. As the saying goes:
"Fortune favors the prepared"
The author is a developer of information systems for online casinos.