For those buyers who take a long time to pay, they can still only receive positive feedback. If a seller writes something along the lines of "bad buyer, took ages to pay, I don't recommend", the buyer can have the feedback removed, keeping the green dot and the seller gets a black mark on their account. The most any seller would be interested in, if they are even bothered to look at your feedback, is your feedback left for others. That's where people's true colours come out.