Steam handles that problem by showing two scores for the item (games in their case): the total score, and the "past 30days" score. This way you can see if something is going wrong recently.
The especially difficult part when it comes to reviews for physical products in that it just isn't sexy to benchmark an old piece of hardware. What makes the situation even worse is that most reviews aren't centralized (that is, you google "productname reviews") and so to a large extent the visibility goes to whoever publishes first. Your brand new benchmark announcement gets clobbered by the pagerank of the reviews that happened right when everyone was interested in the product.