Dismissing the others could be false economy. They might be trying to rip people off, or I suspect in many instances particularly on ebay, they haven't got a clue. A bit like those in the £600 for a Churchill crown thread. You've got to check for mistakes.
What would you do if a listing as a bog standard coin was 10x market value, but the coin in question was an unattributed variety of that basic item usually selling for 10x that of the normal one? Would you cut off your nose to spite your face?
I paid £100 for this (unattributed) one in 2007 having sold an aEF of the same variety for £400. I would have happily paid £500 for it given the one now slabbed MS65, but raw at the time, sold for £600+ hammer in 2003.