Joe, if anyone interested in old guns does not have an opportunity to actually look at many of them, it would be a good idea to use that site and look carefully at the number fonts and the other markings, as well as the general appearance. Quite often one can spot a fake without even a close examination, just by the general look of the gun. Wrong shade of blue, wrong case coloring, wrong grip finish, etc., will almost scream fake. Even some good restorations will be very obviously not "right" to the experienced eye. (Often they do too good a job, far better than the factory did!)
I own some original Model 1851 Navies and several repros, and have seen hundreds of originals. I don't say I can't be fooled, but I have enough egoism to think that a gun that would fool me would fool the vast majority of collectors.
Jim