I don't want to make you cry, but I think it was 
probably real. The seller said that they got it 
(presumably from the studio) as a giveaway at an 
event commemorating the release of the OVA. 
Repros usually have just a number and no letter.

They're probably not a cel collector, and had no 
idea of how much to ask for it. And it looks as 
though the auction ended in four minutes...