Online reviews are a necessary evil for anyone with an interest in electronics or technology, it is where everyone goes to get information. The internet is a powerful tool for anyone doing research, it is also their worst enemy. Knowing where to look and who to trust is important when making purchasing decisions and thankfully, there 
is a lot of good information, from knowledgeable people out there, you just have to know which rocks to look under.
An important thing to understand about even the best made, most loved products is that there will always be a unit with a problem. Not every electronic device does everything well and it is important to understand the strength and weakness of any piece of equipment. Owners who have a negative experience are much more likely to jump online and voice their problem while happy owners sit quietly, enjoying their equipment.
The next thing to know is that people are, well, people and the internet allows them to show a side of themselves that isn’t always nice or even truthful. It is human nature to love what you have and more importantly, to poo-poo the competition.
Shortly after the birth of the internet and the refinement of search engines such as Google, webmasters, retailers and marketers began to understand what a powerful tool the internet is. In addition they needed to devise ways to drive users into their websites where they can sell and market their products. One way to improve your ratings on a search engine is to allow comments and reviews for the product you offer, and this is the root of all review evil.
Online reviews can be very valuable but I have a few rules when I do research. Disregard 90% of the comments on any sales website. Good or bad you are dealing with a high percentage of fan boys and naysayers who may or may not have used the product. Anything written on these sites should be suspect at best. I do pay attention when I see the same comment made over and over however and do additional research on a site with more experienced users, preferably a forum of enthusiasts.
Be it headphones, receivers, turntables, MP3 players or a car, there is a forum of enthusiasts who are more than happy to help you understand any purchasing decision. They will help you understand the real world factors of owning a, b or c product and how one may be better for your system specifically.
When I find a new forum I read through a number of threads to determine the legitimacy of the site. There are good and bad forums. Good forums contain civil, helpful and knowledgeable users. It is fairly easy to pick out the good from the bad based on the intelligence level of the posts. If it appears that every other post is filled with text speak, U R sumwere occupied by teens, which can be helpful but extra care must be taken as a considerable amount of misinformation is likely.
Reviews are not the end all of making purchasing decisions, especially if you are looking at a big dollar purchase or adding equipment that could affect the rest of your system. Any respectable dealer will let you test drive equipment, in your home long enough to decide what is right for you. Take advantage of this to ensure you make the best possible decision for your system. Online reviews are helpful to pinpoint the number of products you need to look at when making a decision but you should never buy blind based on the random information scattered across the internet universe.