You're not selling your body as a product in that scenario no matter how many times you want to repeat yourself. You're selling your ability to pick up a shovel and move crap around with it.
I understand your point, I just don't agree that it's just another profession. I think that old line about it being the "oldest profession" is unproven nonsense, too. It's just some saying people keep repeating. I'm pretty sure our prehistoric ancestors weren't prostituting themselves. There was no money. Prostitution seems to be a feature of stratified civilizations and class. I believe it only starts showing up in first in ancient Near Eastern civilizations. The oldest professions are shaman, tribal chief, hunter, warrior, etc.
To me it's exactly the same thing, you are selling your ability to lay down and do a job.
Accounts of prostitution go back to the sexual services provided by priestesses in the temples of Mesopotamia over 4,000 years ago.
In India, prostitution is referenced in the ancient texts written in the 8th century bc.
And there are many more examples.
So it seems to be if not the oldest then as i said, one of the oldest professions.