There's quite a number of sellers who would 
simply ripped off the sketch when it's stuck to 
the cel and for some I know, threw the sketch 
away. So, you're left with only the cel with 
paint loss. But none are as bad as having grease 
and losing any great amount of paint.

And yes, I used to have a seller who rolled up my 
pan cels. Yes, my pan cels in a thin long 
rectangular cardboard box. Basically, with no 
protection over being squashed as flat when it 
got to me.

I was utterly shocked receiving the 
packet. "Don't tell me the cel is in it" and it 
really was. My heart dropped...

Cels bent and everything... I wouldn't know when 
the painting will start coming off now. This is 
one thing that I hate to see other than line 
fadings.