There are advantages of buying an ex police vehicle as well as disadvantages. If I ever knew anyone who wanted to buy one I'd suggest they spend a week at work with me then they'd probably change their mind.
It all depends on where it came from and what it was used for. Cars to definately steer clear of:
All your 6 cyc models, including your Falcons and Commodores - especially if they're white! They were probably used as a general duties patrol vehicle and would have been flogged. We aren't very kind to our cars that's why they're breaking down quite often. I've seen at least one car come up with the transmission error on the display and put itself into limp mode and wouldn't go any quicker than 20k's.
The SS Holdens (ex TMU) generally aren't too bad. After being in general duties and jumping into an SS I was astounded at how neat clean and tidy it was. Most TMUs look after their cars as they need to be 100% reliable at all times. If there's ever a slight feeling of something not right the car is written off as faulted and doesn't go out on the road until the problem is fixed. They're pursuit vehicles and having a wheel fall off, or similar, at 200 km/h is rather dangerous.
General 6 cyc cars (other than white) would be ok as well as they've been used by other areas of VicPol just for commuting to jobs and other types of transport.
We get rid of our cars once they hit 60000ks. My station just got rid of a BA Falcon thats time was up and by the time we were finished with it, it had a number of nicks in the trim and a very pingy engine.
Also, to put some rumours to rest - Do you really think that a government department that's already having its resources overstretched is going to spend $$$ on vehicle modifications? If they were doing that then they'd have enough to buy more cars so we didn't have to use our own cars to go about our work and to attend court etc.