First off, prostitution has been given a bad name by moralists and some places where it is legal is just another job.
Some places sex workers even get sexually intimate with their clients but in the context of therapy.
I was an artists model, standing naked in a room full of people using my body for their art. I wasn't having sex with any of them, but the thot came that I was in fact selling my body on some level.
Massage therapists, another job I have done, has one person giving extreme pleasure to another's body (stopping short of sexual). You are paid to do this, just as a prostitute is paid for the same service that includes sexual release.
So, prostitutes sell their service, which is the use of their body as do a lot of other ppl.