A casino site does not gain trust through running a review campaign, as a matter of fact, some dubious casinos with dubious intent can still run a review campaign at the beginning of their journey to gain users and their trust, but I tell you that it's only a foolish person who will give their trust to the casino simply because they ran a review campaign.
Why not?
It is possible as it is part of their business, so if they keep their promise, pay to review campaign participants fairly by themselves or by review campaign manager (outsource), it's helpful for their reputation.
It's one of ways of gaining reputation but there are more important contributors for their reputation: platform operations: deposit, withdraw, provably fairness and more.