You have no rights beyond the car having to be roadworthy and it actually being theirs to sell.
I think it would be unwise to assume even this in practice – vehicles are usually ‘sold as seen’. One needs to do one’s homework to decide whether the car is roadworthy or not (e.g. get a specialist inspection) and whether the seller is who they say they are, and actually own the car being sold. If any of these prove not to be the case after parting with the money, you’d probably end up having to take the individual to court (assuming you can ever find them again) which wouldn’t be cheap.