Hmm, I do still have a trick that seems to work, when I want people to not pose.
I start fiddling controls at the camera, then tell "continue, I have to set everything before" have the shutter and aperture set for a correct exposure, take out the eye of the VF and start looking the camera like "what the", and then when there is an interesting situation and they don't expect it, raise it and cling!
But I believe it doesn't work as well if you're a very experienced photographer and they do know, you must be fiddling around like a newbie.
I wanted to photograph once some relatives that they were laughing, they seen the camera and put out a fake laugh and was too late, I took the photo. But I could take another one with natural laughs, there was a notable difference between the two.