If you look at the pure mathematical nature of roulette you can statistically prove that the theoretical payout is going to be about 97%. Each spin will have a 1:37 chance of hitting (European roulette). I’ve seen the same numbers hit 3-4 times in a series. Now, that’s the theoretical part. The imperfect world offers variations in the dealers spin techniques, such as speed and pressure, and placement of the ball when spinning etc…
I seem to recall back in 2004 someone getting in trouble for using a cell phone with a laser device that calculated an approximate placement of the ball in order to make the odds in their favor. I can’t find the original article, but here’s a brief report. 10 Amazing High Tech Crimes