Once I was at Shell Moon Market, I asked the guy to fill Rs 1000. One guy started filling and other came to my side window. I was looking at the meter continuously. The guy near me tried to distract me by asking questions like, screen saaf kar don? note 5000 ka tu nahi etc. I did not bother to reply. The guy stopped at Rs 300 and said done. I kept on looking at the meter and said loudly I asked for 1000. The guy near my window said tujhe 1000 ka kaha tha. The filling guy said I thought 300 ka kaha hai. Then the guy near me again tried to distract me so that they could start from 300 and stop at 700 and charge me 1000. I kept on looking at the meter untill it was fill of 700 ( he reset the meter to zero after 300 then).
When fueling was done, I came out of car and caught the filling guy from collar and pulled him with me to the main road and pointed at the building in Moon Market and said I teach there, just one call and there would be so many guys kicking you that you would be confused that which part to save and which not 
I guess these guys are never going to stop their behavior, be it any company (not only shell). We have to be sharp in order to avoid getting ripped off.