As a seller I too used to give feedback once item was paid for. Now I wait until my buyer is happy & leave feedback for me. If they don't leave feedback I don't bother with them any more.
The star system can be useful if you check out your seller dashboard after each feedback has been left. If you get a low star rating it is obvious that one of the feedbacks left for you has given low star rating & if that is the case everyone who left me feedback on that day don't get any from me either.
I know this is punishing those that do, but it is a good way to not give credit to buyers when credit isn't due. This happened to me only today. Lovely feedback saying great transaction. I go to my dashboard only to find I have a low star rating. So that nasty person who left the nice feedback with low star rating does not get any feedback from me.
It is the only way I can see to actually find out who has been a nark & to deal with them accordingly.
So in a nutshell. Buyer gives me good feedback with on change to star rating & they get good feedback from me. If they leave good feedback & my star ratings go down then no feedback for them. It is that easy.