Not entirely sure but when a casino is using a game provider then RTP and such things are not in casinos control. The provider adjust it depending on the game. The casino is only responsible to bring clients in their platform and let the clients to play. Bet history and everything else except customer management are done by the provider.
These days unless you are a big casino, you can not afford your own system. You are just using others API. I guess bet365 are big enough to have their own game engine and sports engine. I could be wrong.
Me also can be wrong based on my opinion.
It's all-speculation and everything is also possible, until now there is no single device/machine that can check the "RTP" like hash-game. So everyone can speculate RTP can be different, it's also still a big mystery for all-slot player.
What can a user do is trusted the platform, IMO providers should make some development progress in the future while they also created a device checker site from their side for users. So, any of these speculations can be gone.