The longer you play in a particular casino the more you can easily notice some bugs or glitch to exploit. Its the same when you play some strategy games today which the longer you learn about the game, you know it very well like its the back of your hand and there could be one incident that you would take advantage to win. Not necessarily a cheat but one example of this is the giveaway where some users are exploiting it.
There is a casino that I never really get to leave and I go there from time to time to check, they don't do give away anymore because its been exploited by users lol Been waiting and seem like they've stopped.
Correct, it may seem impossible not only to find those bugs but to the bugs themselves to exist at all, but as you mention the more familiar a person is with a particular platform the easier it will be for them to notice a glitch they may be able to use for their own benefit.
And a great example of this are video games, in which fans of a particular game are able to break it completely just days after it has been released, as they are experts on finding bugs they can use in order to end the video game the fastest or get the highest score.
Before the casino launches their project, they will release in a UAT or the user acceptance testing that will bring into their Quality Assurance team or the QA to test any bugs before lunching to the production mode. During the live of course, we cannot deny that there's an instance that will show up with some bugs that didn't find in that time, in that case they will temporarily terminate the services of the game and fix those bugs to prevent getting abused by the players.