Personaly, I don't think that writing :
"you are a naughty boy if you resell this cel
as a production one" will hold much results.

What I don't understand is why people doing
fancels can't sign their work or put a mark
so that they can't be confused with a production
one. Doesn't seems to hard to me to paint a
small signature in some place of the picture
that will then be painted over so that it wouldn't
be too easy to remove it without damaging the
cel.

Apologies are fine but it won't prevent people
from doing it again. And that sound a little
like a "fait accomplit" : You may as well
apologies directly for all the time it will
happen again in the future... I am sure that
will be of great comfort to all people that
will buy a fancel thinking it's a production
one and to all people that get their original
cels copied and sold around.

Cheers,
Yann Stettler