you can try scratch remover but in most cases it wont remove key marks so heres what you do, go buy some 1500 grit sand paper and get a bucket of water. dip the sand paper in the water and gently sand along the key marks slowly until the scratch smoothes out. dry off the spot where you sanded, then get some 3m rubbing compound and rub all over where you sanded until the sand marks fade, then apply some 3m polishing compound over it. does the trick every time.