You can always tell how used or abused a dirt bike it by checking underneath it. If you see dented frame tubing or scratches and marks on the engine cases then you know the bike has been ridden pretty hard.
You can't be too picky with older bikes. Discoloration and a little rust is nothing to worry about. I'm more worried about
serious corrosion dents and cracks in the engine cases. This bike is in GREAT shape.