www.kbb.com is "the bible" of used bikes and cars. Always use the "average" shape column unless it REALLY stands out or is REALLY crappy looking. And of course all things are relative beat up 2003 motorcycle is below average where as a 1983 motorcycle in the same shape would be "average".
As with any machine, if you take it for a spin, look for things like slipping clutch, transmission problems, handling problems, etc. Look at the color of the hydraulic fluid-it should be clear to light "tea" colored on a well maintained bike. Darker than "light tea" and the bike is not well maintained in my HO. Ask to see maintenance records. Then if you do decide to purchase, always start with a fresh oil and filter change. That way you KNOW it was done. Maintenance records can be forged.
