I don't understand why one would use FB Marketplace over Craigslist - where one can be (practically) anonymous unless and until a deal is negotiated. I quit my (anonymous/pseudonym) FB account years ago when I found interacting with others was coincident with/highly correlated to unusual/strange activity on my laptop necessitating several 'restorations.'
It appears that one needs to login to one's FB account to interact with a seller whereas one might do so with a seller on CL using any one of his email accounts. As well, these marketplaces seem relatively isolated where with CL I had a fellow in California purchase a part from an old Satellite dish receiver unit that I'd posted to the Hickory, NC list and I regularly see posts (in response to my Saved Searches) from people in all sorts of places - right in one of my email in boxes the day it is added to CL..