It depends on who is doing a review. If the reviewer is glorifying the casino as if this casino is heaven sent to gamblers, while on other platforms it has bad reviews and when you click the casino there is a referral link on it, then its likely the guy is making a lot from referring gamblers and his review lacks authenticity.
A reviewer should call black is black and white is white; if the casino has a bad reputation and you have one reviewer praising it, then the review is a paid one.
Ever since, I trusted reviews coming from forums because these are coming from true users and they are independent, like here in Bitcointalk, highly reputable members will not throw their reputation for small money.