the seller messed up, the part was not as advertised
negative feedback is appropriate
the seller appears to be a standup guy and is willing to refund the money
at which time negative feedback should be removed, AFTER the buyer get's his refund and not a moment sooner
this is what "feedback" is for, to let potential buyers what has occurred in the past AND what was done to rectify the situation
no one can run a business with 100% customer satisfaction, there will always be problems that are out of the owners control, so NO business can honestly have 100% positive feedback