Happened with me many times.
Once SHELL in PHASE IV DHA KARACHI ripped me for 1000rs. Told the guy to fill 1000, he starts filling, fills all the way upto 1000rs. I give him the money and go. A minute later I see the needle only move like 0.2 cm. It wasn't even noticable. But usually after 1000rs worth petrol, my car tank goes all the way to Half tank, but this time it barely moved. I go back and rant. The guy just says hey i'll give you 300rs more and thats it. After 300, he tells me to go and get my sensor checked. Bottom line: Gives me 400rs worth of fuel INSTEAD of 1000.
Another time PSO at Cantt Station ripped me. Gave them 1000rs to fill. IDK what the **** he put into my car but my car started knocking like hell and later I had to get my tank + fueil filter and everything cleaned.
Lesson learnt.