I just wanted to add my two cents for both MGA and Curacao licensed casinos
In most cases the game providers and regulators are the ones dictating the RTP. If you have Netent as an example, they don't want that anyone has a bad experience with their IP's, because games like Gonzo and others are exactly the reason why they, as a company, are that popular.
If a casino has an MGA license, then they have to comply, and if they have a Curacao license, they have to get an additional certificate (ISO/IEC 17025). Both the regulator and the game provider state that Gonzo for an example can be between 95% and 98%, but then it's up to the Casino to see if they want to play within that ballpark.
And any good casino knows that setting a slot game to 95% will lead to faster burnouts and dissatisfied customers, so they generally keep it around 96% or sometimes offer enhanced gams with RTP ranging between 97% and 98%.
This is only true for online casinos though, offline casinos are sometimes going down to 85%, and I have no clue how can they do that legally, but I stopped playing in offline casinos a while ago so I don't care about it at this point.
What I'm trying to say is, every casino that wants to actually entertain their users and become a name on the market will want to offer industry standard RTP's, and if you're following sites like AskGamblers or similar you'll know which ones are legit and which ones are just here to grab your money and disappear after a year.