Depends on the setting. In a nurse-patient situation, you don’t ever bullshit them in the hopes of tricking them into some kind of benefit.

If your grandpa is raving on Facebook about how acupuncture is working better than opioids for post-knee-replacement pain management, then… “Hey that’s great you found something that works for you!”

YetAnotherUser makes a good point about not enabling a culture of scams or pseudoscience as well.

Discretion is key here.