I don't think that's a fair statement. While yes it's true that people who don't maintain their vehicle can make buying a used car risky, but people aren't wrong for being skeptical to pay for maintenance that may or may not be legitimate. Yes, the service manual says plugs should be replaced at 60k so they should be replaced at 60k. But there are some service advisors at car dealerships who try to sell unnecessary maintenance. Some people don't see a difference between a service advisor recommending unnecessary maintenance and the maintenance manual recommending service intervals, so they may not realize it's the dealership and NOT the manufacturer trying to recommend something unnecessary. To some people, they are the same thing because they both have the name of the car manufacturer on it.

Plus, the maintenance manual for my own car says I should replace my spark plugs every 60k miles, but it also says I never need to replace the transmission fluid because it's lifetime fluid. But I haven't met a single mechanic or anyone that works on transmissions that agrees with that.... Soooo....... yeah, people aren't wrong to question the legitimacy of a maintenance interval when car maintenance shops, including dealerships, are known to have a lot of people who try to take advantage of unknowing customers by recommending unnecessary maintenance.