Find and photograph every VIN
Read the number at the lower driver-side windshield and on the driver-door label. Some vehicles also stamp it on the chassis. Photograph each location without posting the number publicly. If a seller will not provide the VIN, pause. For a location-by-location map, use the guide on where to find a VIN — this page is the order of work, not the full location list.
Confirm the 17-character format
Modern road-vehicle VINs use 17 characters and do not include I, O, or Q. Remove spaces and hyphens. Positions 1–3 usually identify the manufacturer, 4–9 describe attributes and may include a check digit, and 10–17 cover year or plant information plus a sequence. Exact meanings vary by manufacturer — confirming the format is not a specification sheet. For what a VIN is, see the definition guide.
Compare the car, the papers, and the listing
Registration, title, insurance, service invoices, and the advertisement should show the same 17 characters. Spacing may differ; letters and digits must not. A mismatch can be a typing error, a replaced panel, or documents that do not belong to the car. Do not edit characters so a tool will accept the number.
Decode identity first, then decide on a history report
Decoding can return year, make, model, and other identity fields. That is not ownership, mileage, or accident history. On VinSentry, the free preview uses NHTSA for identity and make/model/year recall campaigns — not proof that this VIN has an open recall. Accident, title, mileage, and theft records are requested from CARFAX only after you buy a report, and only when CARFAX returned them. When you are ready to run the number, use the VIN check page rather than treating this how-to as the tool.