The Australian Consumer Law does not apply to private purchases so there are no warranties that are implied such a sale. This means that you buy a car as is and its "buyer beware". You must take all precautions and do all inspections necessary to assure yourself that the car is adequate for your purposes and is in good mechanical condition and all the features are in working order.
The only cause of action you may have against some that you purchase a car off, if the car turns out to have defects is if the person specifically told you that it was working when it actually wasn't. This would provide grounds to sue them under common law for misleading and deceptive conduct.
If it's a statutory write off then its illegal to sell it, but if its classified a repairable write off then it is legal to re-sell it as long as it has a roadworthy safety certificate and passes a written off vehicle inspection.
