If you’re seriously considering buying a car, spend £5 or so and get a comprehensive vehicle check done on its registration. Something like https://www.theaa.com/vehicle-check. There are lots of places that offer this service. It’ll let you know if it was written off or has outstanding finance. Compare the chassis number with the one they list on the check, so you’re not buying a ringer. At the very least, if it does show anything you can use it to knock the price down.
Fair play to you for doing this.