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The best way to check a telescope mirror is to point it at a light source and look up through the bottom of the scope (back of the mirror), any scratches or thin spots will be readily visible. A good coating will still be slightly transparent , you should be able to see the fillament on a incandesant light globe. A few scratches or blemishes won't affect viewing but can be a good bargaining point to get a better deal. 10 years is not that old for a mirror and 10" is a lot better than 8".
Rick
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