I have an interested buyer in another country (France). How do we safely
complete a transaction?
Unless you have an exotic or a very rare care, it is more than likely a scam. If you do move forward, only accept certificated funds before releasing the vehicle. Don't accept 'more than you are asking' and give them money back. Again, 99% chance this is a scam.
Until you verify funds you should not let the car out of your sight.