That’s a good question, I’ve wondered that myself.

I'd say it depends. I've seen a few call out posts work but for the most part if an artist is popular enough people will flock to them regardless of callouts/warnings. I suppose for some callouts do nothing but halt their growth for a limited amount of time.

At the end of the day, people support who they want to support, even if they are supporting a not-so-great person.

I'm more of the opinion it's very dependant on who the artist is. BIG artists are likely to be able to weather any kind of callout post unless their behavior is particularly crappy, but small or mid range artists with a habit of shifty behavior tend to get hit harder by them, especially if there are multiple... mostly because there will always be people to flock to popular artists, either by them not caring about said artist's behaviour, or just being uninformed.

I've honestly never seen any on here or anywhere really. The only time I've known of a callouts was between two artists and they just went back and forth fighting between each other making post the the other was tracing or getting another artists to do their work ect, it didn't seem to effect their followers or the work they where getting it only caused the artists involved to become hyper fixated on the other artist

The main reason is probably because most people do not know that website exists. Even if they do if the artist or commissioner in question is on a poorly moderated site or produces enough content competently to get a loyal fanbase of white knights, it ultimately will not matter. Not to mention a handful of them are super duper famous in the fandom, and barring them dying or being arrested IRL, nothing is going to stop them. Kind of like famous people IRL.