Do the checks that the other posers said. Have it hooked to a tractor and hear it run. If you cant run it, don't buy it. Shine a bright light inside the gear box at the oil filler hole , check oil level, rotate the gears and see if any teeth are chipped. If the cutter bar is over filled with oil, that is a sign the bottom seal is leaking oil from the gear box into the cutter bar, especially if the gearbox is low on oil.