The house or the sportsbook only accept bets, they might get some information on fixed games but they cannot control the game. The ones that could potentially fix a game are those who are playing the game, the players, even the coach, and the referees, as their decision making could be vital to the outcome of the game.
^ I am quite curious how they have information on the game, it is probably an insider who wants to make a profit. But that is right, there is no such way that they will get an accurate result, they make it all by there selves. Fixed games are often happening in sports because as for me, they are also fighting their dignity not only for money. If you have a very strong team, it is possible to get lost. However, anywhere as of now, there is always a corrupt.