The idea and quality is the main criterion, about which many somehow forgot.
I saw a lot of good things, which had low sales (not 100 and 50… but 10-15, etc), had no rating, but was potentially commercially profitable and most importantly - unique and super interesting.
P. S. Besides, some people don’t put a rating (when buying items or tracks), because for buyers it’s not so important (if be honest), it’s important for seller, but not for buyers.