Rick is right. The career/reputation risk is not worth it. I simply ask the flight attendant if (s)he is confident of compliance in an emergency situation. If not the passener gets to take the next flight.

I wish there weren't so many flight attendants who fall into what I call the prison guard archetype but training flight attendants is above my pay grade. As long as they obey me I will support them in their interactions with passengers even if I think they are wrong. If I can't trust them to follow my lead in an emergency then I'm making a phone call and one of us is getting a schedule change but that is very rare.