If it's from the studio, it's most likely 
photocopied - more an "enhancement layer" than a 
correction layer - and the cel was probably used 
in the given anime *with* said layer. I have a 
few cels that have those. (One of Diva from El 
Hazard, a Psychic Force game cel of Wong, and 
three cels of Guni from Nightwalker - just to 
call a couple off the top of my head.)

I'm more referring to how people feel about the
"home fix-it" attempts made with felt tip or 
permanant pens. Not in regards to disclosing it 
for resale (which I think is obvious that a 
seller should) - but more in regards to seeing it 
at all. Is it a pro? A con?

I have to admit, knowing about that kind of 
correction in advance might stop me from buying a 
cel. I almost ALWAYS consider it a detriment. On 
the other hand, there's a severity after which I 
won't accept line-fading either. . . I have a 
couple Blue Seed and one Trigun cel that walk 
that fine line between "fine" and being almost 
more line faded than I'll accept. (Lines don't 
like red colors either. o_0  I'm hoping Inuyahsa 
cels were made with a good copier or I'll be 
pissed in a couple years. ^_~;)

I guess I don't mind a little brown if those are 
the lines the cel was born with. ^_^

Many Sharp Smiles,
--Drac (still *huggling* her new cel. . . ^_____^)