You know the ritual. Post the item. Answer "is this still available?" eleven times. Field an offer for half your asking price, payable in exposure and a partial trade for a broken kayak. Schedule a pickup. Get ghosted. Repeat until you give up and put it on the curb.
The existing marketplaces didn't fail because people stopped having things to sell. They failed because nothing in their design makes anyone follow through. No commitment, no accountability, no consequences for wasting a stranger's Saturday.
That's not a moderation problem. It's an architecture problem.