A free in-home estimate feels like a low-risk step. The visitor comes to the house, looks at the water heater and the utility closet, asks a few questions, and leaves a number. The risk comes later, when that number is treated as a fixed price and the paperwork says something different. Before you agree to a visit, and certainly before you sign anything the visitor brings, settle a few points in writing.
Ask whether the estimate is binding
Ask directly: is the number on this estimate the price I will pay, or is it a starting figure that can change after the install? Get the answer on paper. If the price depends on what the crew finds, ask which findings can move it. Common examples include pipe work needed to reach the main line, a longer drain run, or a closet that needs a different layout. Each of those should be named, not described as unforeseen conditions.
Confirm what the visit actually measured
A useful visit records the things that decide the install: the main line size and where the softener would tie in, the distance to a drain, the space around the water heater, the power outlet location, and the spot for the salt. Ask the visitor to write these down and give you a copy. If the visit did not check the drain path or the closet clearance, the estimate is a guess in those areas.
Also ask what water information the visitor used. If nobody has asked where your water comes from or what the hardness reading is, the sizing on the estimate is not grounded in your house. The methodology page on this site explains the criteria we use when comparing providers, and it is a reasonable checklist for judging whether a visit was thorough.
Find out what happens if you say no
Ask whether a fee applies for the visit or for a decision not to buy, and who keeps the written visit notes. Do not sign a work order at the door. Take the estimate home, compare it with at least one other visit, and only then agree to a install date.
What to keep
Keep the visit notes, the written estimate, and any statement about what can change the price. If the crew later says something is extra, those papers are your reference point. The Missouri Water Softener Buyer's Guide walks through the steps from first visit to install day, and it is a useful place to check that nothing in the sequence was skipped.