When and where is the race.
If there is only a small pool and the races is a few hours away then odds could be very different. TAB odds are done on how much is bet on each horse, so the TAB cant lose. Bookies take the risk on the race by paying set odds at the time of the bet. One punter may put a big bet on the horse taking up a lot of the pool. More than likely this would even out before the race starts and odds would be closer.
If there is only a small pool and the races is a few hours away then odds could be very different. TAB odds are done on how much is bet on each horse, so the TAB cant lose. Bookies take the risk on the race by paying set odds at the time of the bet. One punter may put a big bet on the horse taking up a lot of the pool. More than likely this would even out before the race starts and odds would be closer.