Were it me, I would consult a lawyer or pay the fine (the cost will be about the same).
Otherwise, assuming you did not say anything in your ebay auction that could be construed as suggesting they were real (if so, that is illegal & I would pay the fine & consider it a learning experience), I would send them a letter back explaining that your brother brought them back from his tour in Iraq &, based on ebay's note, you realized they were fake & threw them away (ie., they are long gone). It was an honest mistake. Most likely, you will receive 1 additional letter, which I would answer similarly. In most (not all) cases, that should take care of it.