Good morning,
To my knowledge, the end result of the review doesn't really make a difference. The general rule of thumb I always try to follow is if any money/product/services were exchanged/traded then I have to have some sort of disclaimer stating that there was some sort of exchange made in return for the review.
I try to be as transparent as possible in my marketing/SEO tactics. At the end of the day, its going to come back and bite you in the long run.
Consumer Reports became famous because they refused to receive anything for free, and they were able to build trust with the consumer because of that.
EGOL, a active member on these boards, states over and over, that your content will speak for itself. If you are writing content that is worthy of the positive review, it will come on its own. You may need to help push people in the right direction, but I would agree with Houses, that same energy could be put into refining content, natural link building, creative marketing etc.
If shortcuts were easy or better, they would just be the way.
-e