Questions on playing a System that wins

Hi! For example I tried a system on the NBA and bet on an online sportsbook and I keep winning everyday. Do the sportsbook observe the bets you make and will try to find the pattern of your system? Do they have someone ala-Lawrence Fishburne in the movie "21"? Is following a system legal? or will they change their ways so that the system that works in this time will no longer work in the future? Thanks!

if your buying points on the spread like in nba don't buy 3 points all the time cause they will block you from buying points in the future. many sports books only let people buy 2 points this year.