You certainly can ... usually .... but the general quality of their photographs of the mirror is pretty poor (despite the high price tag of the object!), so you may not be able to tell as much as you'd like. But I still think it odd that they don't post one.
I'm not overly impressed by the portrait of Mademoiselle Contat, but she was on the stage in the latter half of the 18th c ..... and I can't see anyone 30, 40, 50 years later putting her in the picture, so it probably does date from that time.
I couldn't actually handle our mirror before buying it as it was hanging so high up and the auction was already under way.
After posting those last pics I've taken it down to give it a good clean and photographed the rear. I could tell that it had probably been re-silvered during some point in history. It shows a lot of age, but still could not pin it down!