In each package I send out I add a small note (I have them ready to go and photocopied) with a small treat. The note says thanks for your purchase. To ensure that i know you've recieved your item and are satisified please leave feed back..and I will do the same for you.
That's actually a good idea...! i too, only leave feedback after i receive it, of course, i do that for other reasons, but i think it is a motivation for buyers to leave feedback, so i can reciprocate. my theory (well, for my case anyways) is that if someone isn't really satisfied with their purchase, but not really OVERLY dissatisfied, they just won't leave feedback, plain and simple. they don't feel a positive is deserved, but they don't want to mark you with a neutral or negetive either (for fear of also getting it back), so they just don't leave anything. in looking at items where people haven't left me feedback (excluding newbies or those who don't leave feedback as a habit), they were usually buyers who had some confusion about the item AFTER receiving it, either they didn't read the description properly, or whatever. i think they feel they're letting you off the hook by NOT leaving a neutral or a negetive, since they don't feel a positive is deserved. that's my theory for some of my clients that haven't left feedback (there's not too many of them, but enough to be a pattern).
i think if you follow some steps above, you'll probably see your feedbacks left increase..
Kat