Theres a mob in sydney that do mobile inspections on used cars. They can usually do them the day after you call up.
I have had them look at a few rotors etc for me that i have been interested in and it is well worth the money.
They do a 5 page report covering everything on the car including compression test etc and fax you the report when it is completed.
Costs around $200 depending on the car. Well worth losing 200 now and get told its crap rather than losing thousands down the track.
They are called stateroads.
Don't try too look at and purchase a car all in the one day. Be prepared to make a few trips interstate to find the right car.