I use to be a tech. My faith in humanity died a little every day due to the stupidity of customers. Its like the average person cannot fathom reading an owners manual or learning ways to take better care of their car. Dont count on them to ever invest time to learn a little bit about the machine they drive.
I went back to doing it as just a hobby. I like it better that way. Put it this way. 5 years ago every idiot with a 1.8L 1ZZ toyota engine would think "its a toyota i dont have to change the oil regularly every 5k-10k miles" and would bring in completed siezed engines only for toyota to warranty them.