If you wish to ensure a good percentage of your customers leave feedback for you then it pays to write a request for it in your information about your item. I would make it the last bit of info in your text so that the reader remembers it. It should read something like this ' I would really appreciate that purchaser leaves feedback as it is such an important part of the ebay buying and selling process. Thankyou and Happy Ebaying!'
This way all your hard work can pay off in hopefully positive feedback! It also encourages you as a seller or buyer to take your ebaying seriously and in turn make a safer and securer shopping forum.