If some casinos offer even small surcharges or just bonuses to some author of a gambling review site, such an author will still agree to post positive information about this casino. But there is also the opposite - some kind of casino can also order anti-advertising of competitors. And also for money. As a result, all information will be so distorted that it will not correspond to the objective picture of events in the casino world at all. So none of the gambling review sites can be trusted.
I agree that there are paid post to either advertise or make an accusation that could destroy the casino's reputation. Hence, it would be best if you would do an in-depth research about the casino you are planning on playing with aside from reading the reviews only on a gambling review site. There are shilling posts and posts written intended to defame a gambling website so that they would have lesser competitor. Anyone can fall victim from these which is why it is still our responsibility to countercheck whether the feedbacks are true or just made up because someone is paid.
It would be hard to verify each reviews since most of the reviews only provide the pen name of the author and not the real name to secure the identity. A person can check it through articles and other reviews on other platforms such as youtube and other gambling site which are known to be reputable of giving true first-hand experience of the players only.