With that above, can FB Market be a bit of a pain at times, sure, but thats not FB, thats people. Yes, you list something, people will want to see how low you will drop. That is part of the game, but it can also serve as a reality check. I dont care what you Paid for you item, I care what im willing to pay you for said item. If I need to pay what you paid, no reason to talk to you, might as well buy it at the store/dealer/Amazon. Also, your $4000 do-dad, that is available from Temu/Ebay/Vevor for $600; yes, im likely to offer 50-75% of what I can get it for on those, not what you paid.
On the flip side, as a buyer, its frustrating too.  Sellers descriptions, bad pictures, not answering messages, and selling something while you are on the way.  Well, yep, that sucks; But if im selling, and you call and want to come look, and some other guy shows up with cash, hes getting it.  I donr know if you are actually coming, or if you will have the money, or what, so...  First guy with cash gets it.  Yes, I would shoot you a message and say "sold" to keep you from driving an hour or 3 for something thats gone.