It's even worse than that. Traditional sports books have the 49ers around 5% chance to win the Super Bowl. So what they are arbing is the difference between what the odds should be 5% and what they are 12%. So in gross terms they will earn 10-12% but one net when you calculate the 5% potential risk of loss they are only earning 5-7%. And the funniest part is they think they are so smart for doing it.