This has been suggested before but in my opinion it would probably not work here at alibaba.
First off, if you exclude 'sellers' of foreign brand name product from the complaints you refer to then you cut the problems reported here down by about 80%. So reports from buyers of those illegal products would probably not be worth much in a rating system.
Secondly, if you exclude problems from buyers of consumer electronics in small quantities which is really not the forte of this site then you remove probably another 5-10% of the problems reported here.
To my mind alibaba is really a website for buyers to find large quantity manufacturers. Perhaps that is changing but it has certainly always been the aim of this site.
Buyers who are doing big business in China and who take the time and risks to find good suppliers are most likely not going to be willing to reveal who those suppliers are by giving them a good rating. This is not like ebay where anyone can jump in and buy anything, this is a career for many people.
I think the solution is for alibaba to become more proactive in taking action against sellers that are clearly not legitimate sellers.