When the winning bidder has left positive feedback for you (you should check every day and send a weekly reminder when necessary), immediately leave positive feedback for them. You can track feedback on you’re my eBay page under “Items I’ve Sold.” When feedback has been received and left, delete the entries from the sold items list.
Occasionally it will take days or weeks after the product arrives before you receive feedback. I’ve noticed that generally this is due to an oversight, vacation, or just too busy to log on and make it happen. In rare instances your weekly reminders will be ignored. After 2 weekly requests for feedback, I’d just drop the issue assuming that the winning bidder is not interested in leaving positive feedback. In exchange, no feedback is left for them.