I'll stop helping at a friend's boundary, but depending on the situation, I might be stubborn and tell them when I think they're wrong.

First to mind, a friend whose boyfriend was abusing her. She came to my place for help and I suggested we talk to some of the expert resources available for people being subjected to domestic violence. Neither of us really knew how to proceed safely, so my pitch was just talking to them would be a good start. She decided she just wanted to go home to him and that "it would probably be fine, she had just overreacted". Of course I didn't force her or call a DV hotline on her behalf, but I let her know going back to him was a bad idea and she could just stay at mine.

He beat the shit out of her. Again. And from that the cops got involved, whether she wanted them to or not. I wish she'd taken my suggestion, but I couldn't make that choice for her.