If you Hit an illegally parked car in Australia whose fault is it?

It depends if the illegally parked car is a danger or interuption to the normal flow of traffic. For instance if someone is parked in a handicap spot illegally, and you hit them, obviously it is your fault. You need to be able to prove that due to the other persons actions of illegally parking, it inevitably led to you hitting their vehicle. Just remember, you are the one moving, and you are the one who hit the "non-moving" object.