I've seemed to notice lately that some people 
aren't doing a good job with packaging lately.  
Not only in the cel world, either.  For some 
reason they think that priority mail box can 
withstand what happens during delivery.  While I 
have yet to receive major damage to a cel, I've 
gotten many manga messed up during ship.  And 
these were from actual anime stores, not from 
ebay or minor anime sellers.

One of my major pet peeves is when people use the 
priority mail box, have it flat for the cel, and 
then use the box's pre-stick stuff as a seal 
(sorry, can't explain it in writing very well).  
I can't count the number of times the cel has 
gotten stuck in between that spot.  Once, I 
didn't realize it, and pulled too hard on the 
cel.  Got a few creases into that cel.  At least 
it wasn't on the picture part.

Sorry to hear what happened to your cel.  Don't 
know what else I could say to you except I agree 
that people should take the extra minute to pack 
these one of a kind treasures a bit better.