TBH I don't ask for details. I don't believe he has ever actually punched her in the face, that does leave marks, he has slapped her, and I know her, and some other woman I have met on the BDSM scene would be OK with the odd black eye or split lip given in the right circumstances. It's their choice and I know it could be an option for them. Most of her current bruising is arms and legs, and like I say, it's restraint bruising, you can't really stop that except by being more gentle, which isn't really the point.
I'm not into ultraviolence, but I'm not going to criticise those who make an informed choice about it. I do know there is a lot of control involved on the Dom's part, I know that my husband wouldn't want to do any serious harm, and he would never hit her (or me) in anger or any other heightened emotional state, he's a trained martial artist so he knows what does serious damage and what doesn't, and is very good at keeping his cool.