As far as I know, all fuel imported into this country has to conform to Australian Standards. Any fuel imported for the major oil companies is tested and should comply.
I don't know what happens with independents.
My opinion? Stick with the major companies as per syncros advice and use high turnover service stations (sorry old name-there is no service).
If I have to buy Diesel, I go to a station where the truckies go. If they sell any crap the truckies will soon sort them out.
Arie