This one happened a couple of weeks ago, but I had a computer outage that same day (I dropped it) and haven't had a chance to post about it since then. I was called to re-key a house. All was going fine until I pulled the first lock apart. It had been re-keyed before, and not in a good way. I called the customer over and showed her everything that was wrong with the lock. The previous "locksmith" had only put pins in 3 of the 5 cylinders and had ground the shear line instead of creating a shear line with the correct pins.
It was at this point the customer told me she had had another "locksmith" out a couple of weeks prior to calling me and had her house re-keyed. Everything seemed fine until her husband got home and tried his work key in the door and it opened. Since the lock only had 3 of the 5 pins the security of the lock was reduced significantly. The grinding of the lock may also have increased the size of the shear line by a few thousands of an inch, which can be a significant amount in a lock.
I discussed with the customer the idea of replacing all of the locks, but we decided that with all 5 cylinders pinned the security would be good enough, even with the compromised shear line. Upon reloading the top pins I realized why the last guy only did 3 of the cylinders. These locks were very old Schlages which had extremely long cylinders, which made placing the middle top pins extremely difficult. It took me a little longer than usual, but I was able to load all 5 of the pins in all of the locks and left the house much more secure than when I arrived.