Reviews that people leave for products purchased are very reliable. As a consumer, I look at not only the start ratings but the comments as well. I look at the other information as well such as purchase date and where they are from. Those reviews that detail a consumers' experiences inform us of the pros and cons
Reviews that appear on the Amazon website cannot be trusted. Companies pay reviewers to write their opinion, which automatically slants the viewpoint, Even if they are not told explicitly to write a favorable review, a writer will likely do so in order to gain favor and continue to get work.
A lot of companies pay people to write reviews for Amazon. If you look carefully, some people never write a negative review about any product. Also, a lot of people writing reviews don't offer specifics about a product, only that it works great. That is a sign that a review is paid. It is important to be skeptical of Amazon reviews.
No, we cannot trust reviews on Amazon. People are paid to write reviews on Amazon, so the actually rating is usually skewed. Additionally, even if the reviews weren't biased, reviews should always be taken with a grain of salt. You can't really trust the opinions of random people. People should seek out expert reviews for products that they are going to buy.