My missus and I decided to sell off a few bits and pieces recently, and we noticed that as Sellers - We had to "chase" the feedback. We wanted to make sure the buyer received the goods and was happy. I'd say one in five will leave feedback.
The missus bought some books (BIN) we paid via paypal (immediately) and within hours, the package was sent and feedback left for us - but we had not even received the package !
The classic eBay issue right now - It is infested with LOW feedback members. They don't reply to messages, leave no contact details and when you claim a dispute through the eBay system - you have to wait a week (on top of the week you have already waited for payment) - and the "second chance" buyer has lost interest.
eBay has gone downhill - They are EXCELLENT and claiming their fees, but when there is a dispute - they create so much red tape you become disinterested and the items go back into storage.