This practice has become so common and widespread that now most people do no really think of it as a big sin. Some get angry when they hear about it, but when it comes to selling their own old car, and they know a person who does that meter tampering perfectly, they justify doing that while also assuring themselves that their car is really great so no harm reducing its mileage as otherwise it would 'unfairly' get a low offer from buyers.
Forget about morality and ethics, as that is not something that is highly regarded in Pakistan any way. This is also totally against Islamic beliefs as well. We all get enraged about many other things when it comes to religion, but this is plain old deception, and the person doing that earns haraam money from which he feeds himself and his family. Don't sell your conscience (or your afterlife) just for a few bucks!