This is lack of experience at its best.
I couldn't believe my eyes today when I had a call out to repair a lock not operating. The client had another tradie out to address a problem where the key could not turn to throw the bolt. The actual problem was the door had moved (which does happen sometimes).
Instead of adjusting the striker to accommodate the movement, the so called tradie ruined the lock bolt by cutting a section of it away. Consequently stopping the bolt from tracking in the lock body correctly and not be able to throw to the lock position.