What is it that you seek? Over maintenance, under maintenance, or just the wright amount.
How many times a year does a vehicle need an air filter? Depends on operational environment, for instance if you have a work truck that is always in the dust or out the fields maybe a few times. But for those who are not in a dirt/ dust/ grass/ grain free environment maybe only a filter every few years. I personally have owned cars for over 7 years and the air filter never needed changing.
It drives me crazy to see how many filters some people have paid for when I go through their receipts from other shops. Other things which are often over sold is fuel injection services or decarbonizing services. Sometimes these are needed services but many times they are just commission driven sales.
Ever been a shop and thought "My car drives just fine... how could these problems exist?"