Tracking? I'm fairly sure the seller is referring to virtual items in a game. Unfortunately seller protections for digital items are still fairly limited. If it's something like a game or book and you can show when it was downloaded and with what IP etc you may be able to win a dispute. If it's gun in CS : S let alone some in WOW or whatever you're probably SOL since it's unlikely you can produce evidence which will be enough for PayPal. Even more so since not only are you not the developer of the game, but they often don't support selling items via third party methods anyway either forbidding it or just telling you not to do it.
Your best bet is to either use a trusted escrow in the future, or only sell to people with a decent reputation for such transactions and just hope for the best. (There are often various third party sites where people can build reputations for such transactions.)
