Luckily ebay wont let you dispute anything for 2 weeks.
If you sent USPS they have free delivery confirmation (if shipped online) so hopefully you got delivery conf. that way you can prove he received it. Just check the tracking #. If it says it was received and he claimed he didnt get it, tell him to take it up with UPS/USPS/FEDEX that is if he had insurance on the item lol.