Unfortunately, the vast majority of mattress-review websites are likely biased or at least have a strong incentive to be biased. Such sites can include those that rank highest in search engines as well as those that claim to be unbiased.
How can you identify these sites and keep yourself from being duped? Keep an eye out for the following.
Biggest red flag. The offering of mattress discounts / coupons to site visitors and or the presence of referral links likely shows that there is direct compensation to the site by mattress companies. (We at Sleep Like The Dead have NEVER had a direct financial relationship with a mattress company.)
Avoiding bias in a mattress review requires more than merely not being affected by financial considerations. A careful methodology is required. If a review's methodology is poor, vague or non-existent, then bias – whether intentional or not – will almost certainly be present.
A central characteristic of being unbiased is to be neutral. Biased mattress-review websites, however, tend to endorse mattresses in some way. (We at Sleep Like The Dead have NEVER made endorsements.)
A WHOIS search allows you to learn “who is” the owner of a particular website. A biased mattress-review website, however, often blocks this information seemingly due to fear or shame. If they have blocked their identity, then you can't find a person's name anywhere on the results page. This often means that the registrant name says “private" and the registrant organization is a domain privacy services company, such as “Domains By Proxy, LLC.”
Biased mattress-review websites tend to go easy on the mattresses they review or at least on the ones they earn (the most) commission from. In other words, they tend to play up the strengths of a mattress while downplaying its weaknesses – if they mention any real weaknesses at all.
If a website reviews / promotes only mattresses of newer, online brands and does not review / promote mattresses widely available in stores from established and traditional brands, then this is probably a red flag. This is because newer, online mattress brands in general are more likely to offer compensation to the review site than are the established, traditional brands.