Look it over & under. Check for oil leaks. Look at the grease fittings for evidence of fresh lubrication / maintenance. Check the oil and hydraulic fluid. It should be clean and not have a burnt odor to it. Try to start it cold and observe how it runs and how long it takes to smooth out. When warm check for excessive smoke or exhaust odor. Remove the air filter element (easy) and check condition, again a sign that the machine has been maintained. Check the tire sidewalls for deep scuffs, tears or punctures, especially the back sidewalls. Ask about maintenance and / or records. Check the date on the battery. If it's original, ~09 it will need one soon. All I can think of for now. Good luck!!
Frank