[BillyCoxDodgers3B]

Back to OP's question.

Regarding Facebook Marketplace & Facebook groups:

Use Marketplace more for cheaper, pedestrian listings that will appeal to a broad audience. Also, this is a good place to list larger/bulkier items that would not make sense to ship. Batches of hobby supplies such as Ultra Pro pages, boxes, top loaders, etc. are good for Marketplace. Monster boxes of junk wax are a biggie, too.

With Facebook groups, do some searching and find the best groups suited to your interests. Then, further refine these searches to cherry pick the groups that appear to have the best group moderation and least kooky members (that last point being akin to rediscovering Noah's Ark).

There are next to no blocking features as on eBay which save you from dealing with lowballers and tire kickers, and Facebook brings out the worst of them. No automatic decline feature if somebody offers five cents for your 1933 Dusenberg. Be prepared for a lot of wasted time and general annoyance. You will be hearing from a lot of people who apparently only started learning how to type in English in spite of it being their first language. Also, nobody is interested in paying anywhere near what something is actually worth unless it's a super high demand item. Few people seem to bother properly reading your description. Things like "PRICE FIRM" and "NO TRADES" are routinely ignored. You'll be offered to swap their $20 item for your $1000 item, or $150 for your $2500 piece. The only thing that can be done is to individually block their incoming messages via Messenger if you don't wish to spend any more time dealing with them. It honestly feels like every buyer on there is playing that asinine game of trying to turn a red paperclip into a three bedroom house by always getting the better end of the deal.

There have been upsides, however. If you are willing to put in all that time dealing with the riff-raff, you can occasionally (and I mean very occasionally) make a great, longstanding connection with a buyer or seller who approaches being rational! I value the few decent contacts I have made through this, so it all depends on how much time you're willing to invest and how much patience you have in dealing with the public. Hey, at least it's free. Then again, I wouldn't pay a dime to use it.