Change Oil of Your Car. How Often?

Nowadays most of the automakers specify 5000 or 7500 miles'
interval for oil change. But most of the shops in the business of
car repair still recommend 3000 miles' interval.

It depends on your driving habit if we wish to decide who is right.
Even if your auto-manufacturer recommends longer interval, it
could be that they are actually meaning it for a driving habit that
does not involve wondering around the city with too frequent
starts and stops or carrying excessive loads. Short (like 1-2 miles)
intermittent trips in too cold weather and long (above 25 miles)
continuous trips in too hot weather (say in California desert) or
any trip in muddy roads may also go against such recommendations.

On the other hand, if your driving habit is quite normal most of
the days, it is good to have oil-changing trips at longer intervals.
This saves your money and wait-time and also prevents some
significant amount of pollution to the environment.