Well when you look that beast over, start it listen for abnormal noises such as the notorious tick, pop, and bang. Check the case fluid level, has it been maintained. Check the seat for wear, if the seat is worn, you know someone has ridden the crap out of it and pressure washed it to hell. Check the frame for cracks propagating from the suspension mounts. Are all of the welds sturdy? Jump up and down on it, is the suspension up to par. Lights work? Brakes work? Does it steer? Tread on the tires, is the any? Have the rims been beat into a rock bed? Is the chain about to go? Has a chain attacked the case? Check the radiator fluid, is it full? Air filter, is it clean?
Hope it helps, good luck on the shee purchase.