For the good health of fuel tank, fuel pump and fuel filter, I would advise to never let fuel quantity fall below 30% of the total fuel tank capacity, let it alone touch the red mark / almost dead level. You can Google the "Hikmat" in it 
(I immediately top up as soon as I see the fuel indicator gauge falling below the mid mark, and most of the times, my car's fuel tank is almost full).
Whenever you go to fuel station for fueling, I would sincerely advise to leave the driver seat and keep a firm look at the fueling machine. Or at least, keep an eye on the machine, if not leaving your ride. It might be possible that someone, a random person, comes out of nowhere, and start talking:
"... Sir wiper lgaa Doon...?" (O Bhai, lgaa do. Ye b bhala koi puchnay wali BAAT hai? Bhala kaun inkaar karta hai?)
"... Sir gee, Tail kaera paenday oo...?" (Bhi meri marzi, Jo b use karoon. Tenu ki laggay? Etc.)
Etc...
And their sole purpose is to play trick, divert your attention, and pour less, or may be even no fuel at all!
If you ever encounter such situation, just check the machine immediately and thoroughly. If the figures are mentioned in rate, quantity of fuel poured (in Litres, etc.), Total amount according to the amount of fuel poured as per rate, i.e. nothing is blank and figures are there in all rows / columns, then it may be Ok. Otherwise, if just some random figure is mentioned in the amount figure, quantity of fuel poured is blank, it means that you have been tricked and fuel has not even been poured.
