We of course have all used the clone stamp tool but have you changed the tools mode setting in the options bar. If retouching something dark like moles or bags under eyes try setting the mode to lighten. The stamp will clone out pixels that are darker than your target area. Use it on darken to get rid of shiny skin. Remember to make a duplicate layer of your background layer so you can play with the opacity of your cloned layer to make it look natural. Also remember to play with the opacity of the clone stamp tool itself in the options bar.