Know what the estimate covers.
The useful number is the estimate for your actual opening and requested work, with the scope clearly explained.
Start with the job, not a generic price
Opening a door, changing which key operates it and replacing the hardware are different requests. A home with several cylinders needs a different discussion from a single door. For a vehicle, the make, model, year and working keys affect what is involved.
Describe the symptoms and desired result before buying hardware or assuming that the cheapest listed service is the right one. The condition of the door and lock may need checking before a final solution is agreed.
Ask about every part of the charge
Confirm any visit-related charge, labor, parts, additional keys and applicable fees. Ask which details could change the estimate after inspection. If additional work is proposed, understand the reason and revised amount before authorizing it.
A useful list for a planned change
Count the affected doors, note any hardware that already sticks and decide how many keys are needed. For a managed building, establish whether you supply hardware and whether the property manager has a required product or key system. These details help compare like-for-like work.