I haven't used Facebook itself for 7 or 8 years now, but had to break down and make a private account just to access Marketplace. For buying used cars private party today, it seems like Marketplace is the only good option.
I haven't had any issues with it. I honestly don't know how locked down a Facebook account can be these days so "ghost account" may not be the right term.
I have my name and a profile photo on there, but I've never posted anything, don't follow anyone, and all privacy setting are set to block me from search, feeds, etc.
I've only ever had one person block me after messaging about a car for sale, and I couldn't say whether it was because of the account or the questions I sent made them think I'd be an annoying buyer to deal with.
Sure, but if you don't use it you just make that worse. Of course if Craigslist had died where you are then there is no choice. However where I live Craigslist is still active enough that I can afford to ignore anyone who isn't there.
In some regions (mine) Craigslist never took off, and now is a ghost town.
I would estimate it gets less than 1% of the traffic of FB Marketplace, in terms of number of vehicles posted. And nearly all of them are car lots, not individuals.