Hello Danydee
I don't think the casinos can make public this information because a variable RTP would mean they are rigged because if you increase the RTP the user will lose more times.
You surely mean decrease!
To be honest, I'm not sure if the RTP is variable, but what I know is that we can search slots by RTP and this way play with better odds. just google rtp-slots and you will find a huge list.
Not all casinos do this, and on top some do not even provide the RTP info !
Most of the slots are provided by gambling agencies that develop these games, and they rent them as a service. They don't have to prove the fairness of each roll because they have a verified license. And this means we shouldn't care about what happens in the backend and we should trust them because if they do something nasty then they will lose their license.
Here's the point,
I've read somewhere here (
https://bitcointalk.org/index.php?topic=5383777 ) that RTP may vary from casino to another and can be adapted to the casinos wants ! In addition in some casinos software is executed under (the website/casino URL), normally it should redirects to the game provider servers, so you know you are running the game from the original makers, but running the game under another (Interface if we could say) there's no more, or any insurance there, and everything can happen.