IMO do not wait until the buyer returns the camera to dispute a paypal claim - the time to dispute it is when a buyer opens a claim and escalates it to a dispute on the basis that it as not as described as they claim.

Paypal give you the opportunity to defend yourself against a not as described claim.  TBH I have escalated a couple of disputes opened by a couple of buyers that were making outrageous, untrue claims that I was easily able to prove to paypal were untrue, and I won each of those disputes.  No-one had to return anything, both claims were done and dusted. 

If you have the original receipt and other documentation that is detailed enough to prove the goods were exactly as those listed and the supplier and warranty were also as described, then scan it and upload that documentation in the claims process, as well as outlining several paragraphs of why the goods were exactly as described, a succinct version of the communication between yourself and the buyer and if there is any other details that are relevant to support the goods are excactly as described. 

I also think it is worth drafting the exact wording of your response to a claim before you enter it in the relevant section on the dispute page, to make sure it is very clear, sounds fair and reasonable and references any supporting evidence you upload such as receipts.  You can then cut and paste a well considered response, and not have to be concerned about paypal page timing out - as does happen  on occassion. 

EDIT - lol OP you have posted whilst I was writing my post - thats good that your feeling better about the matter