I recall a case where a trio of Serbians managed to observe the roulette wheel bias and profit in a short timeframe. From memory their measurements gave them a window of 6 numbers to bet on, so 1/6 odds on a 1/37 roulette wheel. The best part is they were allowed to keep the winnings as they didn't actually tamper with the casino's equipment

https://www.theguardian.com/uk/2004/dec/06/ukcrime.gambling