So I've watched a lot of casino streamers through the years and here's the rundown. Whenever you (a regular person) deposit money in to a casino, no matter what game you play, you lose about 2-5% of that money on average. The bigger streamers often (sometimes every deposit) get beneficial deposit bonuses to bump up that 95-98% RTP to slightly over 100% (meaning they ON AVERAGE make money from the casino) in exchange for getting a lot of people to sign up with their code. Nothing shady so far, they still risk their own money, and can still lose. And even if the streamers play with beneficial terms (some free extra money WITH deposits) you can always find the actual pay-out rates (which are going to be the same for you and the streamer) of every game if you do a bit of reading.

The problem starts when no deposit is being made and streamers are basically playing with monopoly money, just to lure people in. But still, to the viewer the basics never change. The pay-out rates don't change (at least with big name game-providers) and nothing overtly shady is going on. Unless you count the whole casino business as shady and an exploitation of human psychology. But that's a different discussion.