Paying the review campaign participants doesn't prove that the casino is fair and trusted.
It contributes to a company reputation somewhat, and if you say it has zero contribution to a company reputation, I disagree.
Even a scam casino can pay its review participants; that's not a big deal.
As said, reputation of a company comes from many factors, not only from a review campaign.
Also, I feel that those who are a part of the review campaign will mostly give positive reviews because they care more about the money than the honest reviews (in case they feel anything bad about the site).
Anyway, still I believe that a review campaign is helpful for the casino.
Review campaigns with an approach to open for positive and negative reviews are good for all companies to improve their platforms and products. Through reviews, you can know what are your platform and product weakness that you internally fail to see it, and you will be able to improve your platform and product after that.