The poster had bought on e-bay a coin which was said to have been issued by this monarch, who was also alleged to have been one of the three kings who visited the baby Jesus.

Ah, but my suspicions would have been raised by the mention of the three kings. The Bible record calls them magoi, which is nearer "astrologer" than "king", and nowhere in the Bible account does it say there were three of them, or give any number at all. So, if someone tried to sell me something belonging to one of the "three kings", I would ask them if they were also selling Brooklyn Bridge first.