I sell on ebay and if the package was covered by insurance; which it usually is when shipping FedEx, the buyer/recipient can't file a lost or damaged claim. I don't know how old this post is, but your son has to contact the seller and the seller must file a claim to FedEx.
FedEx will then investigate the matter and make a desicion. Mean while, the seller should issue a refund for the item, as they wait for the insurance claim to process.
Ebay usually has a buyer protection program that protects buyers from situations like this. If a seller ignores such a problem, you can open a case with ebay and they will take action against the seller to get your refund.