I understand what you are saying and making every relationship transactional is certainly not what we should be aiming for. On the other hand, these people did not have a personal relationship. It was already a form of a business one.
What I find problematic is the husband's belief that he owns his wife and her body. He could certainly have expressed discomfort with the situation, but really why - other than old patriarchal notions about women and wives? And it should have ultimately been her decision and maybe if they had the kind of relationships were it was, they would have stayed together longer.
She's comfortable with her body and thinks that largely one naked body is like another. It was clearly no big deal to her and she wouldn't have been compromising her own integrity to do this. The guy wasn't asking to touch her or have sex with her. What really is wrong with him wanting to see her naked and being willing to compensate her for that privilege? Nothing, except for societal mores about women's bodies not belonging to them.
That's the way I see it at least, although I appreciate your perspective as well. I write a lot about how patriarchy brought about class stratifications of all kinds when it emerged 6-9 K years ago, and how power differentials between men and women is just one small aspect of it. I'd prefer not to live in a world of dominators and the dominated as well.