I think parent means "paying somebody so that you can physically use their body".

Clearly, paying somebody to use their own body to e.g. pitch hay for you isn't much different from paying them to use their own body to do any other kind of physical labour for you.

Paying people to be physically intimate with you is definitely different. But it's worth considering cases that don't involve sex: carers dress you, they wash you, including your sex organs and your arse, and they clean up after you.

All that is definitely physically intimate - arguably much more intimate than a 15-minute bump-and-grind session with a person that despises you.

If the two parties consent to the action and transaction, there's no business difference. governments have just decided one action is illegal while the other not.

I don't think that distinction is useful on this question. Lots of non-sex physical work involves just being present, and lots of sex work involves skill.

> Paying somebody to do something physical and paying somebody to physically use their body are two completely different things

I think if we were to explore and expand on this we would find the distinction to be non-existent. How and in what way are they different at all?