I've had some painful lessons in the economics of car depreciation.
If you have a brand new Commodore in 2008, and look after it really well, hardly use it at all - you still suffer a lot of depreciation as soon as you buy it, because it's no longer new.
In 2009, it's "last year's", and the 100,000 Commodores made since yours have to be worth more than yours (barring damage or high kms) - that's market forces.
In 2010, yours is 2 years old, and there are 200,000 Commodores newer than yours ... get the picture ?
The place to research used car prices is the Redbook. They give two prices: what the dealer pays, and what the dealer expects to get when he re-sells.
Typically, the difference between these two is $6,000 - which is the dealer's margin.
So, the trick is to buy where the dealers buy - at the auctions.
I've bought my last three Commodores at auction, and I've helped a few mates through the process. Where I go, the dealers have reserved seating, so it's easy to see where the bids are coming from. I get my catalogue the day before, and research all the cars that I'm interested in, making notes on my catalogue. In my experience, the dealers won't bid above the lower Redbook price, which makes sense. So then, Joe Public fights it out, and sometimes people get very silly. But I have noticed that as the auction proceeds, the buyers thin out: they only have so many places to fill, or so many dollars to spend. Also, the Joe Publics only want one car each, so each winner departs. Late in the session, competition is less fierce, and sometimes you can get a car for the bottom Redbook price, with no premium. That's as good as it gets.
The Redbook value of 2007 Holden Commodore SS VE (checked this morning)
* Private Price Guide $23,300 - $26,100 (what the dealer sells for)
* Trade In Price Guide $18,200 - $21,000 (what the dealer buys for).