We siphon all other fuels out before tuning and put BP98 from the servo at Stapylton QLD. IMO it doesn't matter where you go, you can get a dodgy owner who can do anything to their fuel and 9/10 they won't get caught. But if you go to a massive servo with a huge customer throughfare, you have a better chance of them being clean/good quality as they have a greater chance of law suit if they f**k up and they are more likely to be tested more often than a small local servo out the back of black stump.
If you are absolutely anal about your tune or the fuel you are running on, buy a bottle of VP Racing octane booster. It costs $20 and will certainly make up for any bad batch of fuel you put in until you can get your regular in there. If you are in a remote area and you are suspicious of the fuel being provided, write a letter to your local member or advise the office of fair trading and see what they can tell you. We shouldn't let these dodgy operators continue to provide poor fuel, we pay enough for the damn stuff!