Bidding War at It's Worst: Opening Bid = 1 Euro, Bidding War started at 20 Euro's and blew up to 480 Euro's plus 16% commission plus shipping (apx $580)
Looking closely, only bidder two was upping the ante. Bidder one upped the bid exactly one second later each time, so I assume he or she had made an enormous top bid to begin with, probably 500 euros. Probably never anticipated it would actually go that far.
Indeed, that was a classic duo bidding war! Two people who each recognized the value of the coin, each had the hots to acquire it, and each had the deep pockets to take a stab at it. This type is apparently very rare. There are none on ACS. And RPC Online cites one lone example -- and it's in a Berlin museum. So, for a collector of Gordian III coinage (and there are quite a few such collectors), this listing was perhaps a once-per-decade opportunity... or even... once-per-lifetime? I wouldn't necessarily suspect shilling. But rather . . .
Before the auction I researched and valued the coin, based on prior similar purchases, and I was nowhere close to the hammer price. I have numerous rare coins (1-4 known examples) of various emperors or relatives and I have never spent more than $150+- on a coin. At this price it probably won't take long before additional specimens show up at 1/10 the cost. I agree some Gordian collector really wanted this one, hope they don't have bidders remorse.
I wouldn't criticize, as both bidders might be collectors of Gordian III and only pretend to add new coins to their collection, and not to sell it´ That said, I would never get that coin for that price (but it's just me)
I can certainly understand these two bidders. If it is a must have rarity for a specialized collector the price can get very high. Last year I ended up paying almost thousand dollars for a small bronze of Marcus Aurelius from Caesarea Maritima. By all means not a rare emperor or city but it was the best known coin of a very rare type.