Some service contracts set rules about the car's condition when the contract starts, and those rules are easy to overlook on a busy sales day. For a used car, the condition on the day you enroll is the baseline that everything later gets compared against. If nobody wrote it down, you have very little to argue from.
You have two routes. You can do the walk-around yourself, or you can pay a mechanic who is not connected to the seller to inspect the car and write a report. Each route produces a different kind of record, and neither one is automatically the right one for your car.
A walk-around you do yourself costs you time and nothing else. Take timestamped photos of the odometer, the vehicle identification number plate, each tire, each body panel, the dashboard with the engine running, and any visible fluid under the car. Write down every warning light, every dent, and every repair the seller mentions. Your strength is control: you decide what gets recorded. Your weakness is that you cannot see underneath the car, and you cannot judge a leak, a worn joint, or an old repair that was never documented.
A paid inspection gives you a written report from someone with a lift and trained eyes. Your strength is depth and independence. Your weakness is that the report was written for a buyer, not for your contract, so it may not record the points the contract cares about. A mechanic who has never read your contract will not know to write down the mileage in the format the form asks for.
Before you pick a route, read the contract's eligibility and enrollment sections. Look for any form that asks about condition, who signs it, and whether it wants a mileage reading as of a particular day. If the seller offers its own inspection, ask whether it is the same thing as an independent report or a sales step. If the terms are unclear, ask the provider in writing what documentation it accepts for the car's starting condition. Its answer belongs in your file.
Whatever route you choose, the list of things worth recording is short: the odometer, the tire tread as far as you can judge it, any visible leaks, warning lights on the dashboard, existing repairs and any recall notices you were told about, and the name of anyone who inspected the car. Keep a copy of everything you hand over and everything you are handed back.
Providers that post a sample contract make it possible to read the condition and eligibility sections before you ever reach the counter. They are listed here: vehicle service contract companies that post a sample contract you can read first.