Had an encounter with a Porbeagle shark once, I was in waist deep water with my friends swimming around in some deeper water off the beach. I see the fin in the water, shout to them, and they all rush out. I can't swim so I'd have to try and scramble out, possibly tripping and getting myself into trouble. So I stood still, and watched it.
The Porbeagle swims to where I am and slowly circled me, clearly looking to see what am I. I just keep calm (despite my brain trying to conjure up horrible images of being eaten and dragged away), and slowly turn my body from the waist up and my head, keeping an eye on the shark.
After a couple of minutes (it felt longer), it turns away and swims off. I watch it go, then head back onto the beach... where I had a little freak-out from the suppressed anxiety attack.
I knew if that shark wanted to hurt or kill me, it could have easily done it. In a way, I felt it knew I was trusting it, and that it could trust me.