If you must buy something from Facebook, use specialist groups that are moderated and preferably private.
It's still filled with obvious scams and reporting them does nothing. Meanwhile FB's AI Algorithm bans legit posts for selling prohibited items :D
Also, I quit Facebook before they added marketplace so I can't make a comparison. I'm just going off of this thread mostly. I also know people who sell things on marketplace fairly regularly / successfully.
Marketplace
That aside it's funny because I have the exact opposite experience. It's the best place to buy and sell locally. Not every place has Craigslist (for better or worse) so it's good to have at least an OK digital alternative. I use it pretty much every day.