I have a few with stuck sketches but I like the 
cels too much to attempt an unsticking ^_^  My 
favorite is of Ryo from Devilman and I almost 
never see cels of him so sketch or no sketch, 
hell or high water I got him!

I HATE line fading and missing paint, though.  I 
just got a Nightwalker cel for Christmas from my 
Dad that had some TERRIBLE line fading.  Another 
one had some paint chips missing.  He ordered it 
off of a store online that shall remain nameless 
but has disclaimers about the state of their 
cels.  Since I had specifically sent him a list 
from that store because they've always been easy 
to deal with and friendly I was very 
disappointed, but now I have the cels and I'm 
doing my best to love them! ^_^

Anyway, the point of that story was that 
sometimes you don't know the state of the cels 
until you get them or they're gifts (or both) 
and then they're a part of your collection.