If it is the camera and you have been promised a refund [etc] if you change your feedback I am afraid the likelihood is - to say the least - "remote"; it is an old trick.
If you use Paypal to get a refund you can register for the postage to be paid to China
If it's the neg ask the seller to send you a Feedback Revision request. Tell them to go to Site Map, bottom of any page > scroll down past the categories, to Feedback > Request Feedback Revision.
