Some may not know how to post a review and it is not important for them to do so.

You are right; thats why I have requested to include completed projects of programmer in profile even if buyer do not review. So, there will be less loss by no review.
Please vote here if you like my idea:
http://feedback.scriptlance.com/topic/86150-completed-projects-but-not-reviewed-by-buyers/

Yes, something like this.

On clicking Rating; it should show projects without review too, so buyer can see what work programmer has done(Paid+ Complete)