Same as Zengetz,I have seen the filling station guys doing such practices,once I too felt the same:
I with my friends went to the filling station and asked him to get the tank of my Innova filled with a diesel of Rs 1700.The cashier guy tried to get me involved in gossip saying 1700 to the filling guy who was being noticed by me.
I didn't came out of the car and saw that just before us an Indica got the fuel tank of it filled with Rs 500 diesel and the guy who was filling,even before asking me put the fuel gun in the filling point of my Innova and started filling,I asked him to stop as I saw what he did because my car got a diesel of Rs 730 in just 5-6 seconds.
I:"Oye,tune mujhse poocha ki kitna daalna hai(Have you asked me)"?
He:"Apne unhe oth bataya na ki 1700 ka hai(you told the cashier that 1700)".
I:tune mujhe zero dikhaya?(have you shown me Zero)"?
He:"Maine kiya tha tune nahi dekha(I did,but you didn't saw)".
I caught his hairs and gave him an extremely tight slap with my friends also coming out and started giving him a body massage.Then came his friends and manager to rescue and manager said "I am calling police".
I:"Call right now,I'll see which policeman will arrest me,but this guy will be burnt alive today in diesel itself".
He:"Saahab galti ho gayi wo dhyaan nahi raha,mein dobara bharta hun.(Sir,it was a mistake,actually I lost my concentration,let me fill it again)".
Got the car's tank full and left the place but from the same day,till today the same guy fills in my car but never forgets to show me zero nor he fills without confirming from me..amazingly his concentration has also sharpened..
so what I want to say is that,be strict at the filling stations and if you find them at fault then never hesitate to punish them,even if you are alone then also other people will come for your help because everyone is disturbed from them everywhere in India. Always park your car in a way at the fuel pumps that the machine's display is in front of your eyes and also keep a look at the filling guy or use your left ORVM to look if the fuel gun is there in the filler hole or not.BEST IS TO COME OUT OF THE CAR AND GET THE WORK DONE.
One more such instance which we faced at Haridwar(Uttarakhand):
We friends were on a trip to Mussoorie and were going in a Fiat Linea,so we decided to visit Haridwar too while returning.We stopped there for filling and what we saw was really a new and superb cheating method(this one is applied mostly by the pumps on highways where there is no long line for filling):
There was a Delhi registered Swift VDi carrying a family,they all were in the car and guys were filling the fuel,what we saw was a good 5 liters canister kept behind the Swift with a pipe connected to it and the diesel was being filled in the canister instead of the car's tank.As we entered the pump,the third guy standing there saw us,took the canister and started moving.We went on and stopped him saying "Give us half of that else we will tell the Swift driver".Suddenly one of our friends saw a good beautiful girl in the Swift and heck "He shouted..".
Result:Neither the girl was impressed nor we got 2.5 liters of free diesel...
so at the petrol pumps with very less vehicles or nobody seeing,just take care of this too.