Contact them and ask them how they would like to proceed ... Fix or Return for Refund or maybe even a partial refund ..
Paypal and ebay will take there word for it and you will be forced to accept a return either way so by you taking care of it you may avoid bad feedback ..
right or wrong doesn't matter on here just rules....
FYI if they file item not as described you can opt to have them pay return shipping but if they are familiar with ebay and paypal they can send you an empty box and as long as the tracking shows delivered Paypal will refund their money ...
Best option play it safe and just be nice and bite the bullet ..