Valve have said in a blog post that they have developed a tool that can identify off-topic review bombs and then remove them from the overall review scoring of a game. Players and developers have constantly complained about negative review-bombing which affects their user scores greatly and affects their overall sales due to the reducing scoreline. These review-bombs happen in a short space of time and can really have an impact on whether someone buys a game or not.
This has been in the pipeline for a little while at the request of many players and developers and Valve have given an example of how to the tool works below. It looks for an amount of activity in off-topic reviews and highlights them. In accordance with your preferences it can then exclude them from the overall review score giving you a the score without the review-bombs. Personally this is a welcome tool as it adversely affects developers where review-bombing happens through no fault of their own, it also puts Valve in the good books of developers if this works.
Valve have stated the following in their blog:
Once our team has identified that the anomalous activity is an off-topic review bomb, we'll mark the time period it encompasses and notify the developer. The reviews within that time period will then be removed from the Review Score calculation.
You can read the full blog post here.