Having worked in the petrol station service industry for many years I can confirm most of the facts given are true.

Vapour recovery, (removing petrol vapour from your tank as you fill) does reduce the amount of fuel you have bought. We commissioned one of the first filling stations with vapour recovery, (installed mainly to passify local residents who didn't want the smell of petrol) after four weeks we switched the vapour recovery off to see if the locals would notice the difference. They didn't but surprisingly the tank gauge leak alarms went off on all tanks because they weren't getting the input from the condensed fuel vapour and so showed a loss!

We had one operator who had a couple of hundred filling stations, he always made fuel deliveries in the hottest part of the day and within hours we had to attend to see where several gallons of fuel had gone to. The site operator had dipped the underground tank before and after the delivery and dipped the road tanker before the drop but immediately noticed that the underground tank dip didn't show the same amount of fuel after the delivery. The loss was due to cooling when the warm delivered fuel mixed with the cold product in the ground. The fuel in the underground tank will continue to shrink in volume for a few hours after a delivery so keep your eyes open when looking to fill up your car.

'Splash fills', where the fuel hits the fuel in the underground tank pushing a pipe full of air immediately stirs up the sediment and causes masses of bubbles in the tank which turn to vapour. You can actually see the vapour pouring out of the vent stack when this happens so the same thing obviously occurs in your car tank.

Not opening the nozzle fully takes longer but does give you more fuel! When carrying out measure checks on the pumps we always did fast and slow 40 litre measures. Some flow meters leak a tiny amount of fuel past the piston under pressure so a slow flow gives the proper measure of fuel and a small bit of leakage. If you open the nozzle to full flow the meter seals are under minimum pressure so you get exact measure and the rush of fuel into your petrol tank will raise maximum amounts of vapour which will escape into the atmosphere or be sucked back to the underground tank by the vapour recovery system - 'thank-you very much'. It usually pays to always use the pumps nearest the kiosk. They get most useage so their meter seals wear fastest.

Flow meters are set at exact measure then a seal is fitted to stop any tampering with the setting. Unfortunately some meters then wear in and start to give reduced measures after a few weeks. Other meters will start to give fuel away after a few weeks so it pays to shop arround and note where you get the best volume/mileage results. The difference between meters can be as much as 5 litres on a full tank!

Not many people are aware that there are Winter and Summer grade fuels. The difference can be sufficient to prevent the Winter unleaded fuel being pumped from the underground tank in warm weather. Believe me this has happened. We tried everything from a replacement petrol pump to fitting temporary above-ground suction pipes without success. Finally we dropped a few thousand gallons of Summer grade unleaded into the tank and the tanker was then able to extract the mix and take it away for treatment. In very hot weather when pipes run just below the forecourt surface the fuel can cavitate and comes out of the nozzle in fits and starts. The air separator in the pump should remove the gas but might let some through.

Another legal 'tweak' I have seen is with blended fuels. Usually the 2* and 4* fuels, when mixed 50/50% give a legal octane rated 3*. If the 4* fuel has a high octane level then you can alter the mix to give as much as 75% of 2* and still stay legal!

In Conclusion:

Petrol is very volatile and will evaporate away rapidly especially if you heat it or stir it up, the rate of loss will increase dramatically. So think carefully when you handle it - its too valuable to waste.