Which auctioneers have you heard of in the Brisbane area? Hey top dollar is a relative term. Getting what I paid for it would be a plus, getting substantially more than what a salesman will offer for trade is a mandatory.
Do you have Pickles up that way? It costs a bit to sell at some of the auction yards - but some have no sale no charge. If you put a reasonable reserve on it you can get some bids from punters and if it fails to reach your price you can work with the highest bidder if they are still around.
From memory it can cost between 300 and 500 to sell a car via auction.
The car yard buyers are there all the time and will be the bottom price (often better than what they offer as a trade in price), then all you need is a few private buyers to have a bid and you get a reasonable price for your car.
Get lucky and 2 people are after what your selling and you get a very good price.
Private sale should always get the best price for your car - but can cost a lot in adds if you run them for 4 or 5 weeks with an over priced offering. There is not too many buyers out there at the moment and those that are buying are driving the prices to what they want.
My brother just picked up a black VE Calais with the V options with 13,000 kms for 28k. (car yard)