$45 for a Yashica is a great deal. I have 4 myself -- bought pretty cheaply, but not as a cheap as that! Like others, I would recommend running a roll of film (slide film preferably) through it, going through each shutter speed/f-stop combination. You should be able to cover all speeds on one roll of film. In all likelihood the slower speeds may be a little off, but not by much. I wouldn't worry about the scratch, although if you can find a lens hood (any brand) to cover the taking lens that should help you against any flare.