It's not a problem anymore (since about a week ago or so), but on eBay the case used to be that you could buy something from someone, and only until you gave them positive feedback would they give you feedback. Why is this? If I purchased something from them with no hiccups (practically paid for the item as soon as it was won), they already know that I am a 100% good buyer on my end.
They obviously just waited so that if you gave them negative feedback for whatever reason, they'd neg you too. So in a sense, there was less motivation to give negative feedback, due to fear.
Glad they've changed that now.