Risky To Guarantee This 100%...

That guy is serious (from what I know) - I don't think he would sell a fake coin voluntarily.
The coin looks fine to me, albeit the weak strike on the face side.

Glad to know the seller is reliable and that he stands behind his coins. The king punch looks quite different from the Ponterio coin, and the rim looks rather uneven. The ribbon behind Charles' head also is missing some usual details in an odd way. The devices in the shield also differ from the Ponterio example. It would seem possible for a different king punch, but one would think the lions and castles would correspond on these coins.

Pretty much ALL of the 1790 Potosi pieces are weird/mushy, and they're not in very high relief, which exacerbates that look. The shields are normally crude (as was also often true for the 1770's and 1780's Potosi pieces)... Another quirk with the 1789 and 1790 transitionals is how the planchets are wide (relative to Mexico), yet even so, the obverse design as displayed is too large for it proportionally. Combined with the usual slight off-centeredness, you get this huge motif running off a large planchet.

Hi Swamperbob,

If I had to pick just one feature of the ebay coin that looks wrong, it would be that the castle in the upper left of the shield cuts into or overlaps in the shield border. If there's anyone's opinion I'd consider definitive on this, though, it would be yours. Thanks for taking a look!

The one general question that this discussion of the Potosi mint brings up is: What happened to their quality control? Gilboy seems to concur with earlier authors that the quality of the Potosi "dos mundos" coins is very high, and their equipment and facilities were the equal of Mexico City. What led to this precipitous decline in the quality and consistency of their coins by the 1780s and 1790s? Any information would be very appreciated!