On top of what Iron Flatline said, also make sure the Aprature ring moves properly. It is one thing if it is stuck on A (when aplicable) but a hole diffrent thing if it's stuck at an F/stop or worse yet completely free.
And I will repete the thing about the caps.....I have bought lenses with out them be it with a camera or just the lens it self. It gets irritating trying to decide what lenses to take because you only have so many caps.