Are you sure that isn't a guest cel? The update 
at Usagi's House said "Guest Cels" so it may just 
be ISL's cel for sale. Why don't you write to 
Usagi's House and/or ISL and ask them...? Also, I 
have been doing business with Usagi's House for 
many years and they are friends of mine. I have 
never seen them sell a Repro cel without 
announcing that it was a reproduction (for 
example, Saiyuki and Fushigi Yuugi 
reproductions). So, I seriously doubt it's not a 
real cel. And the prices are high because 
Gravitation cels are very rare, very beautiful, 
and in great demand.

I would make sure you get the facts directly from 
ISL & Usagi's House.

-m