I'm surprised that it doesn't happen a lot more.
When we were there last year, a guy gave me his phone to take a picture of him near the edge.
He kept stepping back closer to the edge. He didn't speak English, and I tried to motion for him to step closer to me (away from the edge) and the guy stepped back even closer. I thought I was going to watch him go over. We had taken a tour there, and after I handed the camera back to the guy, I looked at my driver/guide guy, and he was just shaking his head.