You can get extra feedback from buyers by sending feedback mail at right time. Also by giving buyers different scheme like if giving discount for future product. Sellers can also provide free shipping for future products if feedback provided
Have problems with it myself, half won't post feedback of any kind. I even include thank you forms asking for it.
I used to buy cheap item. Such as a bg picture for about $0.10-0.25 each item from each different seller.
If you're a seller, it's better to have more of the seller than a buyer feedback- sell cheap digital products - templates, software, ebooks and communicate well with the buyers.