If your buyer has been in touch to tell you their item isn’t as described, PayPal will help you mediate this dispute and get to a resolution. We recommend you keep your proof of shipping and all other relevant proof, such as for example proof of conversation with this user and pictures of the item, as they might be required for the investigation.
If PayPal verify the item is significantly not as described, they will most likely ask the buyer to return it to you and provide a valid proof of shipping before transferring the funds from your account back to theirs. If they verify this is not the case, they will most likely close the claim in your favour.
If you are enquiring about a case that is already closed, we suggest you contact PayPal directly to try and appeal to their decision, as we do not have visibility over any disputes.