I don't trust good restaurant reviews, and only trust bad ones if they cite specific issues, like using wrong ingredients, etc. I trust my friends and family when they say a place is good or bad much more because I know their tastes and I can ask followup questions.
For electronics, I pretty much don't trust anyone with anything unless something is backed by the manufacturer. I only trust Apple products because of Apple Care. Everyone has had a bad experience with a laptop, a phone, a tablet, a mouse, a USB cable, etc. It's not worth listening to most times since it's usually a horror story from 10 years ago about a company that who's had their entire manufacturing line re-tooled since.
On Amazon for a generic product, the biggest indication to me is if there are lots of reviews. That means lots of people own the product. If most of the reviews are one star, it's a crappy product. If not, it could be good or bad and I personally find very little correlation between the way I perceive a product and its Amazon reviews.
This can provide its own bias. For instance, your average film critic has seen so many versions of stupid action movie that they find those movies pretty tiresome.
My favorite reviews are currently from America's Test Kitchen. Their equipment reviews are especially insightful and well written to provide a thorough expert opinion on products. Wonderfully, they've found a business model that allows for their independence.