In order to make sure that an online casino is reliable, it is recommended to check it on recommended sites that deal with reviews of online casinos, such as Askgamblers and Casino Guru.
Still, you fall again within the realm of trusting a third party about the legitimacy of a third party, it is kind of a redundancy if you asked me. It would be more productive not go to directly for a centralized platform to seek for information about casinos but focus on communities like this one, in which anyone with certain level of experience and reputation could give you their own opinion and appreciation on the casino you are interested in.
I am not implying those websites you talk about and ill-intented or anything like that, but it is not a good practice to completely trust what they say. I have personally seen how good review webpages have been corrupted by services like scam casinos for them to get promoted, since I experienced it, I rather to open a thread in this section and openly ask about a service, instead of reading and review webpage...
Just my two Satoshis, though.
Your two Satoshis are well accepted because from the your point of view, it clear that third party centralized review platform lack the credibility needed to rely on them in making decisions on which casinos to gamble on, because most of them have some bayas approach in operations because as far as they are concerned, the money their generate from the review service is very important for them and for that, they can do whatever is possible just to score good records before the team in other to keep the money coming and they don't care how and what a gambler encounter on those sites, what concern them is the revenue they generate from this service.
This is why some reviews platforms like trustpilot will give positive star rating to a scam casino like 1xbit and the rest of the other scam phisted book maker's and other services providing platforms with bad reputations, so for that we need to depend on our individual research more than depending on others to make such a research and recommendations for us.