Amazon has enacted a rather dumb rule with regard to paid product reviews. I was contacted about a year ago by a chinese company I have bought a lot of electronics from and left positive reviews for in the past. They offered me deep discounts (via rebate) on products if I left reviews after purchasing and using them for a while (no 'has to be positive' strings attached). I reviewed a couple of their products last year and put a disclaimer about being partially compensated for the review at the top. One of the products wasn't great (it was a bottom of the barrel budget phone) and I gave it a middling review.
I didn't hear from them for a while, then about 3 months ago they reached out with two more products they were asking me to review. Same deal. I submitted reviews this time and they got rejected because it is apparently now against Amazon's policies to publish compensated reviews. I resubmitted the reviews with my disclaimer removed and they published them. Kinda crappy on their part that they won't allow reviewers to divulge that information.