I know in the states if you get pulled over by the EPA they can test the emission of your fuel to see if it is not from a legal source, same as they check to see if you have a crate motor or not in your car. As far as australia go, well doubt they have a way of checking...
If we are talking about de-fueling aircraft then it is a common occurrence of sorts and with some of the larger companies it is legal to put this fuel back into the aircraft but limitations apply.