Also, in the end of the day, if a shilling campaign is sophisticate enough then it would not be difficult for some entity to forge those withdrawals  to personal or private bitcoin addresses. Actually, that was one of the tactics which was carried out by the infamous casino 1xbit around here, back in the day when they still cared enough about this place to try to fool more people into depositing money to them: they took two workers of the casino itself and were asked to shill the casino in their official thread and sending images on their withdrawals.
Keeping that in mind I would not even completely rely withdrawal screenshots as a way to verify either a casino is authentic or not, in my opinion.

Though, we both agree it is better just to stick to casinos which have a long history of operations and also have an official representative here in this forum, otherwise, I would rather not to deposit more than a couple or dollars or make use of their faucet feature (assuming they have any, that is)