I like many people leave feedback for people as soon as I sell an item and recieve payment or when I recieve the item that I have purchased. But to my annoynce I find that people cannot be bothered to leave feedback.
What I have now started to do is to check the feedback left by people and see if they leave it for everyone ( I recently bought of someone and have had to ask numerous times for the person to leave feedback, which they have still not left, the person in question has a feedback of 324 and has left 148 for people).
So my advice to people is thus :- when you purchase an item and you fill in the additional instructions box write "that you will not leave feedback until it has been left for you"
when you sell an item put in your ad "feedback left on completion of checkout, Please ensure you leave feedback for me Thank You"
If at the end of the day you do not get the feedback left for you ask Ebay to remove the feedback you left for the person, This counts as a negative for them.
Hope this has been of some help to you...