Paypal would (should) side with you providing you have an admission via e-mail that he has ridden the wheels.
I know the whole ‘side with the buyer’ thing is generally true, but from reasonable experience, stick to:
– He rode them, he would not have been able to ride them if they were like that when they arrived (point out factually, why would he even try?)
– It’s not possible to warp carbon like that though normal use, wear and tear or structural failure.
Keep totally factual – avoid any accusations, just stick to reasons why it is not possible.
Best of luck.