The best advice is just to be cautious. Obviously don't send money before you get something and make sure it's functional. Facebook marketplace is a good place to find deals if you know to be safe.
Not awful. I've had only positive experiences. No buyer protections, but it's hard to get scammed buying something in person from someone local, unless you get it home before realizing it's fake/broken, or they kidnap you and lock you in their basement. There are pretty simple precautions you can take against either, not that there's any foolproof solution...but I wouldn't say awful.