Inceptions
Buyers are not required to notify you before leaving feedback.
Your buyer is obviously very unhappy. I would contact him, tell him you are sorry he is not satisfied with his purchase, and invite him to open a return so that you can refund him in full. (You also pay return shipping.)
Another option is to just refund his payment in full and save yourself the cost of return shipping if you think it's not worth it to get the item back.
AFTER you have taken care of the problem, THEN ask the buyer if he would be willing to revise his feedback (again apologizing for his disappointment in the transaction). He may be willing to change the feedback to a positive (no guarantees however).
