I would disagree that having a setting that tricks people into playing unranked games is good. I don’t think it would really look good for the server either. (While the glicko system can be confusing as apparently it takes a few games to adjust rank/rating, I’ve seen forum posts where people say their rating didn’t change after a game. That can confuse people as is without secret unranked games…)
Regarding the problem of opponents playing differently - I think in part, this is highly subjective. I agree that it is possible that if you know someone is making a series/streaming where they either pretend to be a weaker player or won’t punish mistakes too severely, then maybe you’ll play differently. Or for instance if you’re playing unranked maybe you try some things that are unusual or out there and hence don’t play ‘normally’.
For the first part if you know the account/stream you can probably know what to expect, making a teaching account with hidden unranked games or freezing/resetting a ranking won’t fix that. That’s just an inherent problem with being popular.
However the second part I think is highly subjective: whether you think an opponent you probably don’t know is playing ‘properly’, ‘usually’ or ‘normally’.
Dwyrin had a video recently ( here) where he mentions he was getting annoyed by what he thought was a player who knew Dwyrin was playing for his basics series, and was intentionally not protecting his groups. Then upon further reflection and looking into that players past games realised that said player had lost games due to life and death situations.
My point would be you don’t really have to be well rounded as a player to be an amateur.
So whether you call a game normal based on some notions you have of how an x kyu or y dan should play probably isn’t a good basis to trick people into unranked games.
I think this is especially true if there’s an intended outcome from the games, that surely random pairing and playing with people on the internet can’t always fulfil.