Though you might be a bit annoyed if it turned out to be Robin Gunningham.
Update: "This listing (260720844294) has been removed, or this item is not available".
So now we'll never know!
What it originally said: If you win this auction I will mail you a piece of paper revealing the true identity of "Banksy". I have uncovered his identity by matching up the prices of his sold pieces to corresponding tax records.
The highest offer (after some 20-odd bids) was $999,999:00.