Valve published a quite long article about how to deal with positive "review bombs":
Steam Blog :: Positive "Review Bombs"
It is about the positive reviews that appeared on Steam after Ubisoft gave away AC:Unity for free on uPlay and whether those reviews should be counted as reviews or be excluded with their new "review bomb" policy.
TL;DR: Valve decided that they will not exclude those reviews. Reasons are listed in the article. But the article ends with an invitation to discuss how to deal with it.
Valve also talks about how important reviews are for the sales of a game:
Steam Blog :: Positive "Review Bombs"
It is about the positive reviews that appeared on Steam after Ubisoft gave away AC:Unity for free on uPlay and whether those reviews should be counted as reviews or be excluded with their new "review bomb" policy.
TL;DR: Valve decided that they will not exclude those reviews. Reasons are listed in the article. But the article ends with an invitation to discuss how to deal with it.
Valve also talks about how important reviews are for the sales of a game:
A Mixed game receives over 500% more boost than a game in Mostly Negative. That might seem scary, but we're still talking about a boost that's small relative to many other store factors, and it's the minority case - 71.7% of titles on the Store are Mixed or above.