I have a few extreme cases on my BL.
Like, there was this one player who joined a clear group and watched the cutscene. He said it is a alt but I called it bs to myself but wanted to give it a try.

He wiped us for 30min at the first mechanics and we then disbanded.
The player went on my blacklist.

A few days later I joined another prog group.
It filled and we we didn't queue in. Then someone asked me why I don't answer my co-tank. Well it was the time waster and I didn't notice it.
So I told the group that he is on my BL for joining a clear party without knowing the fight and that I will leave and find another group because he was first in this one.

About a hour later I got a random DM from someone who was in that party and they told me that it was a trap group because of the tank and they did not even got close to the mechanic they wanted to prog.

So he got a little "permanent" behind his name on my .txt blacklist.
So yea, these extreme cases do not work.

But it can also be different.
I've also joined group's that want to practice one mechanic further then I have played, but I only join these groups when I've seen guide's and povs and I'm 99% sure about how the mechanic work's.