There’s always a risk when buying from private sellers so it’s definitely a matter of buyer beware. Private sellers are unregulated and there’s not much legal protection available to you if something goes wrong. Make sure to check if there’s any money owing on a vehicle or if it’s listed as stolen or written off. Also check a car valuation service to make sure you’re not getting ripped off.
Private sellers always have their very own reasons for selling the old cars. So you need to be more careful than buying from a dealer. If you do know cars, go for it. If you know little about cars, you'd better buy from a dealer.