The fact is all the cel sellers get their cels
from somewhere, many of them have been exchanged
hands for several times easily.  And actually,
many websites get their cels from AWS, Commit, 
Zero, Mandarake...etc.  Don't think they get them
directly from the studios because most of them
don't have such luxury connection.  Whenever it 
changes hand each time, most likely, the cels jack 
up each time.  Even for the people who sell their
cels on Yahoo Japan, do you think everyone get the
cels from the studios...NO, they get their cels
from the stores and conventions before too.  And
believe it or not, most of the cels that you 
personally owned have exchanged hands several 
times and have been jacked up several times too.
Unless you buy them directly from the studios,
then you will get the best deals.  Otherwise,
everywhere is the same.