I will be honest in saying the prices on betfair are not always the best, it depends in what price range you are backing, if under 2/1 the better prices are on the TABs or bookies if you can get on.

When you are backing higher priced runners betfair can be higher most times.

I will give one bit of advice, don't use http://racingform.betfair.com.au/ to compare TAB and betfair prices not sure where they get the TAB prices from i think they pull them out of thier ass.