Brokerage Coins

Not "brokerage" - it's "brockage". There's a definition in the CCF glossary, but basically it's similar to a "vise job", except that it's a genuine mint error which did actually happen in the mint. A failure of the coin ejector mechanism meant that a finished coin was still sitting in the press when a new blank was inserted. When this new coin was struck, the previous coin acted as a die, creating a reverse-incuse pattern of the same design which would appear on the "normal" or unaffected side. This side would usually also be in very sharp detail, since it's been struck twice (just like a proof), the second time with twice the thickness of metal in it than usual.

"Vise jobs" can resemble brockages, but a typical vise job will leave telltale traces of the original design left behind; there should be no such "two sides of a coin on the same side" effect on a genuine brockage. The one on the ebay auction linked to looks legit to me.

At the back of the McConnelly "Varieties" book there's a brief half-page summary of brockages, with an example illustrated.

Thanks SAP, always helpful.