It looks a lot like a Batman sketch he did at the 2006 Toronto convention appearance:www.flickr.com

 

Your eyes are definitely better than mine, but there do seem to be some differences in the marker strokes. The question would have been whether it's because of it being a forgery or a bad reproduction (something to do with the photocopying of the original.). However, the crosshatching on Batman's face are definitely dissimilar and the likelihood of my being able to sketch a Batman head so incredibly similar (down to the angle and length of the cape as it trails off his shoulder) is incredibly unlikely. It, does seem to lead one to conclude that it is a forgery.

I'm not sure what I can do to prove that (and I, frankly, don't have the time), but, if you wish to use my statements to report it to ebay, you have my permission.