It is blocked if the seller or buyer don't communicate between the actual sale and leaving feedback - go figure bout the brains behind that ??

That is because when the seller described the item such a way there was no need for questions, marked as posted & sent such a way that the buyer got notice from AP with the tracking number  and there was no need for further communication, some buyers felt that the communication was neither good nor bad and were leaving 3 stars.  I am happy with the arrangement as it is.