When my wife and i moved into a flat, I noticed the lock was nearly done for. So I exchanged the cylinder with something that was a real quality lock, and gave the landlord a copy of the key in a sealed case.

When we moved out, I informed the landlord that we had exchanged the lock because it was busted, and i would replace the current lock anyway - if they provided a new cylinder i would install it for them. They declined and insisted that I install the original lock. They didn’t test it, and had to get a locksmith…