ONLY BUY OR FILL UP YOUR CAR OR BIKKIE IN THE EARLY MORNING WHEN THE GROUND TEMPERATURE IS STILL COLD.
Remember
that all service stations have their storage tanks buried below ground.
The colder the ground, the denser the fuel, when it gets warmer petrol
expands, so buying in the afternoon or in the evening.... your litre is
not exactly a litre.
In the petroleum business, the specific gravity
and the temperature of the petrol, diesel and jet fuel, ethanol and
other petroleum products play an important role. A 1degree rise in
temperature is a big deal for this business. But the service stations
do not have temperature compensation at the pumps.

WHEN YOU'RE FILLING UP, DO NOT SQUEEZE THE TRIGGER OF THE NOZZLE TO A FAST MODE.
If
you look, you will see that the trigger has three (3) stages: low,
middle, and high. In slow mode, you should be pumping on low speed,
thereby minimizing the vapours that are created, while you are pumping.
All hoses at the pump have a vapour return. If you are pumping on the
fast rate, some of the liquid that goes to your tank becomes vapour.
Those vapours are being sucked up and back into the underground storage
tank so you're getting less worth for your money.

ONE OF THE MOST IMPORTANT TIPS IS TO FILL UP WHEN YOUR TANK IS HALF FULL.
The
reason for this is, the more fuel you have in your tank, the less air
occupying its empty space. Petrol evaporates faster than you can
imagine. Petroleum storage tanks have an internal floating roof. This
roof serves as zero clearance between the petrol and the atmosphere, so
it minimizes the evaporation. Unlike service stations, here where I
work, every truck that we load is temperature compensated, so that
every litre is actually the exact amount.

ANOTHER REMINDER, IF THERE IS A FUEL TRUCK PUMPING INTO THE STORAGE TANKS, WHEN YOU STOP TO BUY, DO NOT FILL UP
Most
likely the petrol/diesel is being stirred up as the fuel is being
delivered, and you might pick up some of the dirt that normally settles
on the bottom.

Hope, this will help you get the maximum value for your money.