Most Roman coin fakes are easy to spot once you are familiar with the right "look and feel" of the real thing. When created from scratch the counterfeits rarely have anywhere near a convincing style. Sometimes they get the emperor's portrait more or less on the money (ah, pun) but then pay no attention to the lettering, rendering it in a modern Helvetica when they should have used something more like Times New Roman. Sometimes their best efforts in getting the style down are betrayed by the rest of the coin looking very odd: too round, too perfect, too shiny, too this, too that. A masterly execution in one area is spoiled by an amateurish in another. But sometimes they get everything just right - more or less. From a glance this coin appears alright based on style (click to see it bigger). And for good reason: the style is spot on because the fake was made using an original. As far as I can sleuth out the counterfeit began as a mold being made from an original - and quite exceptional - Aureus of Hostilian. From this mold dies were prepared or, more likely, the mold itself used as a die with which was then driven into a golden blank to create the facsimile. The dies, or mold faces, were pressed using a vice rather than struck by hand - the weak link in the process.
Although from a photograph it's hard to tell in hand the play of light as the coin is moved around reveals lifeless, evenly frosted surfaces where the original would show areas of varying polish; from mirror smooth crevices to the duller shine of the devices. To create this lustrous appearance a coin blank has to sustain the enormous momentary psi pressures of the clash of blank being sandwiched between hammer and anvil. A vice may drive all the macroscopic details faithfully but leaves a soft-focus texture at the microscopic level that results in that frosty look.
When the dies are struck the blank deforms under the pressure and heat generated from the energy forming small ridges or "flow lines" which spread out radially from areas of higher pressure towards channels formed on the surface of the die. Because the relief of the ridges is generally very shallow in fresher dies the subsequent casting process is incapable of capturing these contours very well into the secondary die and when the fake is pressed this "third generation" surface loses even more of this detail. On this coin flow lines are nearly non-existent.
The perfect fake is, of course, the one every expert still regards as genuine so whether any, or even many, are in the marketplace trading with the tacit approval of dealers and collectors is unknowable but it should be encouraging to those on the buying end to know that even when a dedicated effort is expended in fooling us the results are still often too crude to be widely convincing.