Agreed about capitalism, in general at least.
Where it becomes OK, in my view at least, is where there is a degree of consent on both sides, which you don't seem to think is possible. Slavery of course totally lacks consent, so we can dismiss that right away. On the other hand, there are lots of examples of people that are reasonably happy with the "contract" they have with their employers. I have been both happy and unhappy at different times. My first job, after school with an insurance company, paid so little that I could only survive by continuing to live with my parents. Later I moved to another area of the country and got paid enough for my needs and with some left over for recreation. Even later I got into computer programming, which I happened to be good at, and made a lot of money because at the time we good programmers were scarce (largely because companies wouldn't train people, but that's another story). Maybe we were exploiting the employers for a while?
Regarding prostitution, it depends on your attitude to it. If both sides are happy with the arrangement and totally free to choose, I don't see the difference between that and selling hamburgers. But it's an emotional subject and difficult to evaluate without preconceived values entering the picture.