I've had this happen to me and it seems like the 
post office workers are unclear about how exactly 
to go about filing for an insurance claim. I 
opened the package in front of the clerk and she 
filled out the portion describing the damage to 
the cel after I explained that the artwork was 
bent. I did not have to return the cel to the 
seller. Instead, I had to get a receipt from the 
seller stating the amount of the cel (the email 
printout that came with the cel wasn't enough, 
apparently.) I then took it back to the post 
office to complete the filing procedure. In the 
end, I have my cel and the reimbursement from the 
post office.

---Trebuchet