Unfortunately, the answer is pretty simple. Facebook wants you to use the paid advertisements they offer. They still list dealers being able to manually post vehicles as a feature, but I'm unaware of anyone who can actually use it.
Concierge told me multiple things over the last month or so
first they were not sure how to fix my "unique" problem
then it was a well known issue that the "internal team" were working hard to fix
then it was that my account had been put on restricted access for breaking the code of conduct. They were never able to tell my what I had done or what rule I had broken.
I was told to report the problem and I would hear back within 24-72 hours, although that's been 2 weeks or so ( I do go ahead and submit it daily just to hopefully be a thorn in the side)
They may not be bots per say, but they really only have 4-5 canned responses they can spam at you. Each one leads to a deterministic dead end of talking to anyone.
My primary gripe at this point is I have multiple vehicles listed before I lost access to marketplace that I can no longer interact with. Some of them have been sold but I cannot remove them, and I still get messages on them occasionally. Nobody I spoke to had any idea how to remove them...
We honestly had pretty bad roi on the paid ads, best luck of all of them was advertising a single more popular unit - basically paying to run a single marketplace ad, which I wouldn't even have too big of a problem with doing in general, if only it wasn't handled so shadily.