Well, you do! If your car's mileage is bad, it means you will be spending a lot on fuel. Moreover, it means that you will be causing more pollution and
depleting the world's fossil fuels.
Thus, the government and consumer agencies are very keen to ensure that consumers understand the car's mileage, as manufacturers are always keen to overstate it.
So in current law, the ARAI of India will inform you what your car's mileage is from independent tests.