Short answer to the original question: yes. If it was sent via USPS (rather than a private carrier, as bstreep mentioned), and if they sign an official form saying that they didn't receive it when they actually did, then that is both mail fraud and a form of perjury--federal felonies, big-time fines, and jail sentences.
Have you filed a complaint with Ebay? If you paid with PayPal you can file a complaint with them also. PayPal refunded my money
to me last year when I bought a laptop
off of Ebay and the disk drive, memory, etc. were not what was represented in the listing, and the seller simply stopped responding to my e-mails after I sent the laptop
back to him.