How do you know those listings are all scams?
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
Both of the people you listed have accounts from pre-2010, and the first lady at least (Jodi) looks undeniably like a real person with real friends.
EDIT: OK, the fact that they both have the same car listed in 20+ areas across multiple state boundaries is absolutely suss. I'm still confused as to where these accounts came from, though. They can't be fake. Were they maybe hacked?
Sellers seek the highest price the market will bear. If the price is unusually low, it's either a scam or there's something wrong with the item. There are some rare exceptions, but it doesn't average out in the buyer's favor.
50% doesn't strike me as exceptionally low. I've sold things for much cheaper because it's better than throwing it away, and still I get faced with tire kickers who keep trying to negotiate it then insist on some other pound of flesh when I don't budge on price. It's why I avoid used item marketplaces.
Many people sell for just above trade in value because that’s what they are being offered by a car dealership. That’s often 80 percent or less than private sale price.
Other times they just need a specific amount of money, which happens to be substantially less than the item they are selling is worth.
Other times, the seller is not the one that has to purchase the replacement. Phones are good examples here. A lot of people get a new flagship phone every year. Sometimes it’s just because they are bad with choices, boyfriend, etc. these people often sell their old phone for substantially less than market value.
People are frequently not rational actors.