I don't know of any studies (do you?). Do people only look at the star rating? We have done some statistics and found that star rating only tells a small part of the story. Anyone with a background in statistics knows this, though.

My personal strategy is to ignore all the good reviews. I already know why I'm interested in something. I want to know what other people think sucks about that something, and then I decide whether it is something that would bother me.

People are naturally more vocal about complaints, and if they have a serious gripe then they are far more likely to speak up in a negative review.

If they like something, that is basically meeting expectations and there is no urgency to seek resolution. So I expect a larger percentage of positive reviews to be shills, since nobody else will feel much need to post anything.

But if the negative reviews are things I don't care about (or are obvious douche reviews) that tells me a lot.

This is my base strategy as well but thinking it through it mostly means that negative smear reviews of competitors should be more "valuable" than fake positive reviews of the companies own products.