Leaving Marketplace reviews is a chore if we have to write something about every last item. For potential buyers, the boilerplate feedback can also drown out useful feedback. Let us click a number of stars, and make the text review optional.
If you prefer to keep viewers visible to combat review stuffing, you could still show who left star-only reviews. Sort the blank reviews to the end, or present them in a concise list format.
It is also worth noting that other major marketplaces like Amazon and the iPhone app store allow star-only ratings.