Roughly compiled from a previous career in the automotive industry. Service jobs are a lot alike when it comes to customers.
Technosavages - minimal knowledge of how things work
"Ever since you changed the left rear brake light, the right front brake rotor has started making scraping sounds. I know you broke something."
A) A tail light runs off the electrical system and is turned on by a switch attached to the brake pedal. That is the only connection to the rest of the brake system. B) Sounds like you're due for brake pad replacement which was noted on the work order when you had the brake light replaced.
Give a deep internal sigh, educate them a little, quote a brake job and thank your service writer for noting the brake condition on the preliminary writeup.
Malcontents - never happy with anyone
"The last mechanic who worked on my car ripped me off!" More service writer discussion brings out that the potential client has never had a good relationship with anyone who's worked on his car.
You start to realize the best way of handling the situation is to turn down offering to repair the vehicle as you're next on the list.
Freebie Hunters - out looking to see if they can guilt you into more free work
"You worked on my car, told me the distributor was worn out and that the emergency repair wouldn't last very long. Well it's been nine months and its doing it again and I think you should fix this for free as it should last longer than that." Hmm. The repair order here says we thought it would only run for a month or two while you saved up for a replacement and you were to bring it back 7 months ago and get that taken care of.
Documentation of your work is a very good thing, indeed!