Speaking as someone who has punctured a tire or two on in-ground lifts (I even did it once on my own car), and who has been known to close a garage door a little too early (hey it's cold out there you know and these little heaters don't quite warm up the shop like they used to), I can be very sympathetic with the occasional damage.
However, like Doug and RPMGeorge said it really comes down to tracking the occurances by tech to see if there really is an on-going problem with carelessness.
At the end of the day, I used to sit down with the tech and ask what went on. It was as non-confrontational as possible -- just trying to get to the bottom of what caused the problem (was it a bad part, do we need better tools, do you feel rushed, do you know what you're doing, etc.) Their attitude normally told me the story -- if they were overly defensive then they probably messed up and are covering up something and I need to watch them. If they accepted what went wrong, then I figured they'd manage their own behavior to make sure it didn't happen again.
I did have one tech that we ended up having to let go because of the damage he was causing. He had worked at every shop in town and his nickname was "Cross-thread Dave." Ol' Dave would cross-thread an oil drain plug if you didn't watch him. As we realized what we needed to do, I began saving his little botch ups. Sure enough, Dave dragged us into the state for unlawful discharge, but we brought all of Dave's handiwork with us. Some of it was so obvious that the judge saw our point, and after seeing 5-6 examples of problems my service director just looked the judge in the face and asked, "would you want Dave working on your car?"
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** Rob, Editor WD&S **Help is only a message post away!
robc@dealersedge.com