you can do that. sometimes USPS flops on updating their system.
@Hennessy
my bf and i bought a laptop in early january and i mailed it to him via USPS. the package contained the laptop + a pair of shoes so we bought insurance worth $700 with signature confirmation.
it never got to where he is in the east coast. it took us 3 months to get our money back.
call the USPS customer service (1-800-275-8777). if you haven't spoken to a human rep yet, always say "customer service" after each prompt. however, you're gonna have to wait ~an hour to talk to a representative.
even if your insurance was only $50, just try to file an insurance claim. if the insurance thing doesn't work, just use the "money back guarantee" thing ebay has so the buyer can get his money back.
and yes, some post offices are sort facilities as well.