Real estate term referring to a house so dilapidated that even fixing it UP wouldn't make it attractive.
Amelia: "I'm sending you a listing of a fixer-upper. It needs a lot of work but the price is good and so is the location."
Bob (upon receiving the listing): "You've gotta be kidding me, Amelia. Looks more like a fixer-downer to me. Take another gander."