If he returns them without going through Paypal and they have been used inform him that you have had it verified and can prove that they have been used so do not qualify for a refund and you will return them to him on receipt of $XX to cover delivery.

Tell them that if they should try and claim through paypal you will provide them with proof of them not having been returned in unused condition.

If they open a Paypal dispute before returning them then you need to be very specific about how they were exactly as described and you are prepared to provide a Stat Dec confirming that those were the only ones you had so must be the ones shown in the picture. I would also phone Paypal, be nice but firm, and tell them that the buyer is just after a refund and that the items are exactly as described and if they do find in the buyer's favour and give them a refund you will be taking the case to the ombudsman.