I would consider getting someones info for facebook to get to know the buyer/seller better. The only dangerous side to this I see is if you send them money via Facebook and with-in 3 days they do a charge back. Paypal processes the payments that go through Facebook and their marketplace. I like it because if I buy an items via Facebook Market Place and the item ends up being broken I have 72 hours to file a charge back and get my money back. So if for what ever reason they claim the goods were electronic they would probably win the case and if there was any value on that account it will probably be liquidated at that point. Just my opinion on the topic.
I used to back in the early 2010s, there was a huge amount of scammers. It's likely not as bad now, since Facebook has been cracking down on fake profiles a bit more. Still though, there's no reputation system on Facebook as far as I know, so I'd be cautious.
From what I have seen the Marketplace doesn't allow digital items, I tried to post a listing for a membership code and it wasn't allowed. Groups or pages can be good places to get customers though.