While you have a house edge, you need to deal with the possibility of shelling out money regularly. This is especially the case if an underdog wins a popular game that people bet on- one event can cost you thousands. Luckily, successful bookies can make anywhere from $5000-$10,000 in a single week.
Bookies are usually paid a commission at the end of every week on their total books losses. From interviewing a variety of bookies, these commissions often vary from 10-20% (let's assume 20% because those are the ones that I have seen more often).