You can tell by click on them. Has a combo of these things: only one pic that is zoomed in a bit, price, they are on vacation mode, no license plate (different from blocking out license plate) etc.
For example: https://www.facebook.com/marketplace/item/497875541786220
or: https://www.facebook.com/marketplace/item/635418997520898 This shows same make a model, there is only one listing is NOT a scam in a 20 mile area: https://imgur.com/a/LSvw42t