Interact with the Seller Directly
Always schedule a meeting by phone and be sure to ask questions about the vehicle you wish to see. Be cautious about a seller that insists on doing all the interaction through messenger. That is not a definitive proof of a scam, but such behavior is suspicious. You will need a phone number in case you encounter a problem while on your way to see the vehicle.
Also be wary if the individual with the marketplace listing wants you to interact with a third party. This scenario removes the benefit of being able to examine a Facebook user profile. The more information you have about a person who is selling the vehicle, the better your chances of avoiding a scam.