Two personal observations, if you read the 'positive' reviews closely, you can sense they do not really like it, but yes, they don't want to piss off an advertiser. I always look for reviewers that buy the equipment or the equipment they already own that they are obviously happy with already. And, although it's true they can't review everything thing, I always watch for brands they don't review, or a brand that has a nice selection of items, but still don't get review. Also, if the equipment has alreayd been review by another mag/blog, they may not brother to review it. I do not believe they are rating junk or even average equipment as five stars or whatever, as their own reputations would get destroyed eventually. Several mags and blogs have gone under in the last 15 years.
Not perfect, but if they didn't take ads the subscriptions were would ten or twenty times as much. I base this on professional publications that get no little to no ads.