That wouldn’t necessarily help.

^ This. My ex roommate had her ex girlfriend steal the work paid cell phone and she was able to get the serial IMEI and MEID to the police, and the police returned the phone. Also if it's an iPhone, use the find my phone app from another iOS device or from their website and mark it as stolen ASAP. Do not erase the phone though, it should be safe under a lock screen. Unless you never locked it under a pin... Do *not* remove the iPhone from your iCloud account though! Even if he erases it by a computer it will start up and ask for your info and he can't put in his iCloud info. It makes the phone a brick where he can't get past the startup screen. Look up iCloud locking. Also see if your phone carrier can help trying to lock it down or to issue you a new phone through insurance you paid for. If your phone was an android you'll need another expert. And save all Facebook marketplace messages to try to track the man down/prosecute him.

Aside from meeting in a crowded place, meet inside an actual building or anywhere but a sidewalk. It is for your own safety and bring someone with you. I have sold a few items before and had someone come with me to either a cafe, subway station, or somewhere with security cameras (i.e. outside a bank). My buddy is always someone who is a fast runner and have a chance of taking the other person down if something goes wrong. Do not be afraid to suggest another place if you are not comfortable with the place the other person suggested. If the buyer/seller is that interested, he/she will be willing to compromise the location.

Not everyone automatically thinks the worst of people and this doesnt make them a bad parent. Also not everyone thinks someone who's name and photo is in their inbox is going to steal something they are selling, that's not smart on the thieves part.

Some areas, including my own, are asking people to do these exchanges in their lobby to prevent this and other crimes because not all people think the worst. Unfortunately, bad things do happen and it’s best to always be prepared. Op is lucky it was just a stolen phone. I’ve done parking lot meetups. But it was mutual friends of people I trusted and knew would help track them down if they ripped me off. I also knew his place of business and took my rather intimidating looking husband. Not saying op deserved it. Nobody does. Just happy it wasn’t worse.