: Close all windows and doors for a few minutes; if the interior smells strongly of mildew or, conversely, of heavy cleaning chemicals/deodorisers, it is a major red flag.
: Selling a flood-damaged car is incredibly difficult; most dealerships will not take them as trade-ins.
: Problems from water damage often don't appear immediately. You might drive the car for six months before the electrical system starts to "ghost," leaving you with a paperweight.