You can't help yourself

Despite your efforts to keep a straight head, your other head starts to drive your instructions to Beth. You have her push up her own tits for a couple pictures, then ask her to bend slightly at the waist for great pictures of her cleavage. Then you circle around her to take pictures of her ass, even going so far as to spread her ass cheek with one hand and snapping pics with the other. You can tell she's beginning to get uncomfortable. In the back of your mind, so are you at the loss of control.

"Hey uh...is it ok if I smack your ass a bit? I need a reddish hue for this exposure..." you hope she accepts your lame excuse.

Beth pauses before replying, "I...uh...I guess. You sure we can't get some makeup or something?"

"I'll be quick," you say before slapping her ass a couple times, alternating cheeks. You risk going a little harder and Beth yelps, tears forming at her eyes, so you back down. You take pictures of her red ass, focusing on the handprints you just left on her. Standing straight you give her one last slap, turning it into a grope as you squeeze one ass cheek. Beth's face reddens but, surprisingly, she doesn't protest. You adjust your cock before directing her to lay down. There's another moment of hesitation before she complies.

"Alright Beth, I need some sensual shots, you mind just rubbing yourself?" you ask as if asking her to masturbate in front of you was the most normal thing in the world.