A locksmith working on a parent's side door is being let into a home the parent has, in some sense, refused to let anyone into. That is why vetting matters more than the quote. Judge the business on what it will put in writing, what it will check before it works, and what record it leaves behind.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Ask for the paper before the visit
Ask for the business name, the street address, and any license or registration number the city or state requires. Then check those numbers yourself with the issuing body rather than relying on what the business sends you. Ask whether the technician carries liability insurance and whether that coverage extends to damage to the door or frame. Ask for a written estimate that names the service, the parts, the labor, and any trip or after-hours charge. A verbal number is not a record.
Check how they verify who is asking
A careful locksmith asks the person requesting the work to show identification and to show that the property is theirs or that the owner has authorized the work. That check protects your father as much as it protects the business. If a company will open or re-key a lock for anyone who calls and pays, do not hire it for a home you do not own or manage. Ask directly: what do you require before you open a door or change a lock at a home?
Ask what they change and what they leave behind
Ask whether they will re-key the existing cylinder or replace it, and how many keys they hand over. Ask who receives the keys and whether the business keeps a note of which keys were cut and for which door. Ask for a receipt that names the work done and gives a phone number to call if the lock fails in the following weeks. A business that leaves no record leaves you guessing later.
Compare the terms, then the price
Put two or three written quotes side by side and check that each one covers the same service, the same parts, and the same callback terms. The lowest total is often the one that leaves out a trip fee, a second visit, or work on the other exterior door. Choose the quote whose terms you can read back in your own words.
For local options before you call anyone, start with Local Help in St. Louis, then check each business against the list above.
Next move: Tonight, call the business you are considering and ask three questions in order: what identification do you require before you work at a home, will you give me a written estimate with every line named, and what record do you leave after the job. Hire the one that answers all three plainly.