We have found that sending a polite message, such as the following, to the Buyer will result in Feedback being left for us. 

. And you will also know that your item(s) has/have been received!

    " - Just wondering if you have received your ..... and all is OK, as they were posted on .......

      - We would be very grateful if you could let us know if they have not arrived and/or they do not

      meet your expectations to enable us to address the issue(s) immediately.

      And, if you have received them safely and all is OK, we would also be very grateful if you could

      let us know so we can go ahead and leave Feedback for you."

Our Feedback increased by 99.9%.

Good luck!