They absolutely want a level playing field in terms of the integrity of the game/match/race, whichever the case may be. Without it, they stand to lose large quantities of money as well as a significant portion of their customer base. And yes, they will adjust the betting lines as money comes in, but that has no bearing ensuring integrity of competitors.The betting houses do not want a level playing field. They want a level betting field. They'll adjust the odds until they get it.