Most the time by user experience.

Policy "KYC" and withdraw experience activity, how fast the withdraw will be sent. In here, we have a few good website with high withdraw activity and the process is almost instant. Compared to website review, I most of the time prefer user experience.

Search on google or forum with "SCAM" word + casino name, how the case is being handled by the site and progress. You also need to follow the progress case too, sometimes user makes a false accusation just because they doing some activity against term & condition.