You've never had a to file a claim with the USPS?
I hope you never do.
They are a bear to deal with. You have to prove the value of the thing your filing the claim for. It doesn't matter if you buy $1000 of insurance, you have to be able to prove that's what that thing is worth.
For example, you send out a set of valve covers that you powder coated. You buy $1000 insurance policy.
They get lost or damaged, you the shipper must file the claim, not the receiver. Now, you have the obligation to prove that the valve covers are worth the $1000. Problem is, it doesn't matter that you just did $500 worth of work on a $500 set of covers, the covers retail for $500 and that is all you will get. Oh, you mentioned to the clerk they came to you to be powder coated? They must have been used. Well, that means that they have depreciated in value. Now, you need to prove the value of used covers. Come back with an estimate, they found a cheap pair for $25 on ebay. Guess what they'll pay you? On top of that, you will fight tooth and nail to get that paid out.
I saw this play out way to many times.