Most definitely NOT the advertisers who wants to pay the biggest bugs or yielding huge ad click throughs. I would expect Google ranking reviews from more honest sites like consumer reports, BBB, chiropractor reviews etc and supported by articles in good newspapers or magazines. Mattress business is extremely high margine business with their major spend category being ads, not R&D or manufacturing. They almost entirely depends on glossy ads with ongoing war of making outrageously false claims among competitors. Ads are the last thing you want to depend on in this category to make your purchase decision that would impact you for may be half decade.
