The killer feature that Facebook marketplace has is the fact that you can do some basic verification of the person you are selling or buying an item from.
(My sister flips baby strollers as a side-hustle. Seriously. She makes money with it, too. Not enough to retire, but enough to keep her home, raising her kids. She's been doing it since her first child was born 12 years ago, when she realized how expensive decent strollers are. She buys broken strollers for near-nothing, keeps an inventory of her own replacement parts, fixes them herself, then sells them. New mothers love it, because, once again, baby strollers are friggin' expensive.)
It is hard to scam someone with an in person exchange of cash for goods.
Annecdotally, many CL sellers have told me to just get the item from their yard and put the cash under their doormat
You would think so, but some asshole tried to do this to me. We had agreed on a price ahead of time, and when he showed up, he tried to low ball me with a 50% lower offer. I refused to sell the item to him, and then he became aggressive and I had to call the cops to get him to leave.
I won't get into the details, but based on what I saw, I think this guy runs kind of a side-business acting as a middle man reselling tech gear. I think he does this routinely, probably low balls people and then tries to re-sell the same stuff on marketplace afterwards. I think tech gear attracts assholes/scammers more than anything else because it has a potentially high resale value.
So, just be careful out there. Never share your phone number with people from marketplace, and don't reveal your home address if at all possible. Try to have a friend over if you have people coming for transactions or do it in a public place.