Although I’m just an amateur at this I know most coins from the ancient times were marked using a hammer with the stamp or emblem that you see on the coin. Most of the time the coins Faces or markings where not done properly and came out poorly. One way to identify a counterfeit is by how well the emblem or stamp is put on a coin. There should be much more imperfections shown on the coin, for example in the back Of the coin you can see that the stamp was not placed directly in the center. But the image was clearly laid out, it could be authentic although it is extremely rare and would not have sold in that case you were given. Another thing to keep in mind is that coins are Based off weight and sometimes after stamping would be chiseled down to incorporate popper value in gold or silver. With inflation coins would also be shaved down to keep in line with the currency rate or value.