If it's the one pictured then there are a couple of items of note. That is not a pre model 10, it is a post-war Military and Police. Not exactly the same thing.
Also, and I really don't want to sound mean, but the photo doesn't look anything like a S&W Model "X." It clearly predates the model numbers. I would put some of the responsibility on the buyer in this case, assuming the photos were available. Sure, the seller misrepresented the gun, but Caveat Emptor is a phrase that is old enough to still be spoken in Latin, so as consumers it is up to all of us to do our homework.

What if we flipped it around and you got a pristine Registered Magnum for the price of that post war M&P? We'd all be high-fiving and congratulating you.

Again, I am not trying to be nasty on this- chalk it up to a lesson learned.