I don't think the problem is with pointing out
it is a fancel...but calling it "fake" is a little
too strong...

Those that don't read Japanese may get the wrong
impression that the seller was trying to sell them
as production cels.  This wouldn't be good for the
sellers reputation.  They weren't trying to pass
on the cels as production cels and as far as I can
tell...the *are* cels...fan cels, but nevertheless
cels.  

Maybe it would have been better to just give
people a heads up that those were fan cels and not
production cels.  In anycase, people *should*
always use a translator...lots of auctions have
important information in them.  Such as matching
or non-matching background, defects, cost of
shipping...etc.