Though cheating in casinos is illegal, more and more players and even dealers try this method of "making money". However, this is totally illegal and the person found doing that will definitely be answering to the police. If you happen to think that you can cheat without being noticed - remember, due to the use of modern technologies it is impossible.
Past posting is the way of cheating at table games like blackjack, craps and roulette, of course. The thing cheater does is placing a bet after the dealer has announced "No more bets!".
In roulette, past posting is placing a bet after the ball lands in a pocket. After the ball lands, the player has to distract dealer's attention to move or place the bet on the winning number. Most of the time, past posters play in teams.
The player that won a past-posting bet places some bets more but without cheating and leaves the table.
All in all, this method of cheating as you can see could only be done at land casinos. We used past tense to underline the fact that modern cameras and other security devices will not allow players to cheat like this.