If the seller hasn't contacted you yet then try using the option to contact the seller and say something along the lines of "I left you some feedback for an item I purchased recently; however, I inadvertently selected the Neutral button when I left my feedback. Could you please send me a Feedback Revision Request so that I could amend this and upgrade my feedback to Positive?" If you were to do this then the seller may well realise that you made a genuine mistake and send you a Feedback Revision Request so that you could revise the feedback you left originally. If he does then you can upgrade the feedback rating you left for the seller and it will then show up on his feedback history as a Positive feedback, as opposed to a Netural.
