Re: Don't hire the firees
I used to come across precisely the same thing when working in the support team for one of the handful of UK suppliers of an obscure system. Several times an incompetent support contact would get dismissed from one customer, only to turn up at another a few months later.
One was a particularly irritating person who couldn't do anything right, and ended up at three different customers of ours. One call alone, pertaining to him not being able to get our system installed on a new server due to a hang on booting, took up all of the day, due to him being totally unable to tell me the last line displayed on screen when the system hung. I forget what the actual problem was, but it would have been something to do with an incorrectly configured device driver.