Other than pump calibration,there are obvious figures which are easy to manipulate......so a gas station owner calls a Tech and asks him to manipulate 500,1000,1500,2000,2500,3000....The obvious figures.Anybody who attempts filling at this prices will not get the right quantity of fuel.How to beat the cheats out of their game????......SIMPLE.Always have some loose coins/notes with you and whenever you request for a re-fill,make sure the attendant understands.Ask,say for fuel of Kshs 1045...1736,2023,3007.....Two things will happen,the attendant will act surprised or will salute you.......after you have left.

Beware when you check into a petrol station and the guys jump at you asking in haste mbele iko poa? fungua tuangalie and cleaning the windscreen while u have said weka 1000/= If u don't pay attention to the guy dispensing the fuel, you may get conned nicely.
I had a cousin petrol attendant who told me how they do it. But the worst fuel theft happens to company fueled vehicles using vouchers, cards and the like.