Does the spare behave the same way?
If another key works better, mention that difference. A worn or bent everyday key is a different starting point from a lock that resists every key. Keep the troublesome key so it can be examined, but don't keep forcing it.
Say whether the change was sudden or gradual. A key snapping, a handle becoming loose and a bolt catching more often can all be described in plain words. You don't need to open up the mechanism to make a useful request.
The open-door clue
A bolt that moves easily with the door open but catches against the frame when closed can point to a fit issue. That doesn't identify the full cause, but it explains why a new key may not be the answer.
For a security door in front of the main entrance, make clear which lock catches. The two doors may have separate wear, alignment and key questions. Our opening guide helps keep them apart.
An exposed entry should also be considered as its own setting. Product suitability, finish and care depend on the actual hardware. Desert surroundings don't mean that every stiff lock has the same weather-related fault.
What would a repair achieve?
The useful result is a lock and door that work together as intended. Ask which part needs attention and whether a repair can provide that result. If replacement is proposed, understand the reason and what the new hardware changes.
Changing who has access is separate. If an old key should stop working, rekeying may need to be discussed alongside the repair. It shouldn't disappear into a vague description of fixing the lock.
At handover, check the agreed keys and operate the lock with the door closed as well as open. Explain any movement that still feels different. Keep any care instructions specific to the fitted hardware instead of applying a treatment meant for another product.