Maybe she was trying to walk out the shop with an armful of stuff because he wouldn't give her a refund. Maybe she was taking the value of an exchange.
Maybe she hit out first.
Either way, that's all irrelevant because he's practically twice her size and grabbed her by the throat and dragged her round the room.
My dh is bigger and stronger than me. If, big example here, I were to hit him, his response wouldn't be self defence, or attack, he doesn't need to defend himself, I can't inflict any damage. He wouldn't raise a hand in any way.
This woman couldn't do anything to that man so his response should have been to block the door and call the police if he had an issue, not start attacking the woman like that.
I hope he loses his business and gets prosecuted.