Prior to working on Guru, I just assumed that online reviews were true. Then I saw the jobs - "Wanted 500 positive reviews."
Recently, in a sting operation, the police set up a fake restaurant on a review website. Sure enough, they got several negative reviews. I am not surprised. I was checking out cabinet builders as one of my jobs and some of the bad reviews were over the top - I highly doubt the guy came back to your house after the project was done and kicked your dog... sorry.
I only give honest reviews. People cannot hire me to write a review for them. One time I did bid on a job wanting someone to honest review a book for her. She gave me two of her books for free. Then I realized she wanted the reviews published because someone had put a nasty review about her on Amazon. I checked and for whatever reason this guy was allowed to publish a comment that insulted the author without having read the book. Nowhere in the review was the book addressed, he just complained that the author was giving away free books in return for a review.
My sense of justice was offended. I took no other payment from this author except the books, and I wrote an honest review on Amazon for her - "My daughter liked the book" (it was a picture book). I gave her a generous review if for no other reason than to counter the injustice of the other persons nasty comments about the author. However, I also complained to Amazon about this guy - to the best of my knowledge they never removed his comments.
I have several reviews of books on Goodreads as well, but I did not review either of the books I received from the author mentioned above on there. I want people to know they are getting my honest opinion - not my paid opinion. However, I see nothing wrong with an author giving free books in exchange for an honest review. How else is a new author supposed to break into the market and how else are readers to know if the book is worth their time?
That said, I do review books for a professional book review site. When I post these reviews on Goodreads, I preclude my review with a notice that I reviewed the book professionally. I get paid all of $1-$10 per book, but I do it because I can be completely honest in my review. If I think the book was awful or needs work, I can send a message to the author instead of writing the review and explain the reason for my dislike.
When an author begins to pay people for a good review or even for a bad review of a competitor's book (as opposed to an honest review)- that is when I have an issue. And, when a someone pays for 500 generic product reviews that the reviewer has neither tested nor even knows what they are reviewing - then I have a serious problem. Granted, most authors would not want to pay me for an honest review - it takes a lot to get a 5 out of 5 star rating from me - my average on any review is 3 of 5.