Given how messy the relationship is between products, sellers and fulfillment on Amazon, I don't think it realistic to expect customers to know which to blame. For example, I received clearly counterfeit merchandise. I don't know if it is the sellers fault for providing counterfeits, or Amazon's fault for commingling stock. I don't know if the product reviews are exclusive to that listing or if they will be applied to other sellers listing the "same" product. And in the end I don't care. I just want others to know that if they order from this listing they may get counterfeit goods. Product reviews are by far the most consumer facing information, and most of the other feedback mechanisms that Amazon provides seem to go into a black-hole where no other customers can see them and which Amazon never acts on, so it is natural for customers to use product reviews for any type of feedback.

There are a few things that Amazon could do to improve reviews for sellers. They should make seller reviews more prominent in listings. And if a review is determined to be posted to the wrong place (product vs seller) Amazon should move it to the right place instead of deleting it. I can't see the issues regarding fulfillment feedback ever getting better though. Late shipping is one thing, but reselling returned items and commingling good and bad inventory will always be opaque to the customer.