I may be shot by some of the TA's who visit this site with the following comments, but hey....
TA's are useless for domestic bookings. Book your tickets through the carrier direct. Use a website such as
www.quickfare.com.au to get the cheapest fares and book away.
You could possibly get a few $ off your fare through your TA if you flew Business around Australia, but even then it wouldn't be much discount if at all.
Qantas is 9000x more efficient than a TA for a domestic booking. Got a problem? Call Qantas at 2am in the morning - they'll help. Get to the airport late? No worries. Talk to Qantas at the airport to sort out your drama. If you book your ticket through a TA, then Qantas doesn't have to help you directly until after you've commenced your journey...
Adding a TA for domestic flights adds no value at all IMHO.
Now, if you have friends with a great corporate discount on their flights, and will book your flights for you - that is a different matter!! I recently saw the prices offered to one corporate for flights, and was very impressed. Wish I could get them to book my leisure flights, but alas - not possible.