To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
This shelf is fairly light weight plastic. May be OK if you only put a stack of paper on it. But anything with any real amount of weight (4-5 pounds or more) is going to cause the shelf to sag in the middle.