You do not need a salesperson to tell you whether the stairs will take a lift. You need the measurements in your own notebook before anyone quotes the job, because a rail that fits the staircase on a drawing is not always the rail that fits your staircase.
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.
Measure the run, the turns, and the landings
Walk the stairs with a tape measure and write down the length of the straight run from the bottom step to the top. Note every turn, whether it is a curve or a landing, and the depth and width of each landing. Measure how far the wall sits from the stair edge on the side where the rail would go, and check whether the open side has a railing or a spindle wall that would have to come off.
Look at the top and bottom landings for anything that could stop the seat mid-trip. A door that swings over the landing, a light fixture, a radiator, or a heat register at the bottom step can all change where the rail can sit. Ask the installer to show you where the seat folds and where it parks, on your staircase, not on a sketch.
Check the parent's part of the fit
The lift has to fit the person who uses it. Watch your parent sit down, stand up, and turn on the seat at the level they are at now, not the level you remember. If your parent has a therapist or a clinician who works with their mobility, ask them to watch a transfer onto a seat before the order is placed. Whether a lift is safe for your parent is their clinician's call, not yours and not the installer's.
Read the weight limit printed on the seat and compare it with your parent's weight plus anything they usually carry up or down. Ask whether the seat has a belt, a swivel, and a footrest that folds clear of the bottom step, and whether your parent can reach the controls without leaning off the seat.
Check the house and the power
Find the nearest outlet and ask whether the lift needs its own circuit or a power change. Ask where the battery charges and what happens in a power cut. Ask the installer to write down the top and bottom controls and where each one is mounted, so a person in the house can run the lift without guessing.
Ask whether your city or county requires a permit or inspection for the install. Call the local building office to confirm. Do not rely only on the installer's word for it.
Keep the stair clear enough for a person to walk down it in an emergency. Ask how the lift parks when no one is using it and whether it blocks any part of the staircase when parked.
Compare the written quotes line by line
Put each quote side by side and check the same items in each: the rail, the seat, the install, the power work, the service visit, the warranty length, the removal if you move or stop using the lift, and who repairs the wall if it is damaged on removal. A quote that leaves out removal or wall repair is not yet a finished comparison.
Ask whether the company rents or sells, and read the return clause before you sign. Ask who answers the phone when the lift stops and how long a service visit usually takes to be scheduled, and write the answer on the quote.
Name who owns the lift after it is installed
Name one person who calls for service, one person who checks that the seat and controls work each week, and one person who can reach the house if the lift stops with your parent on it. If you are at work or away, the backup person needs a key, the controls, and the company's number on paper.
You are allowed to say the stairs are not yet a plan. Measure first, check the parent's transfer with the people who know it, and decide only when every line on the quote matches your own notes. For St. Louis-area programs and contacts, see Local Help for Caregivers in St. Louis.