This device only works if these are two completely equal services served by two equally capable persons with the same investment of time and resources. And it assumes that we mutually trust each other to actually do the thing.

Also, bringing money into the game makes the responsibility stronger. Especially if those two persons are not living in a vacuum, but have other bills to pay [edit: i.e., to make other people do things for them]. Money is there to make people do things more reliably if there is no other relationship between the buyer and the seller.

One could argue GDP measures the degree of financialization of a society more than it measures the presence or absense of abundance.

In fact, Kusnetz the actual inventor of the modern GDP measure said something similar:

“ Economic welfare cannot be adequately measured unless the personal distribution of income is known. And no income measurement undertakes to estimate the reverse side of income, that is, the intensity and unpleasantness of effort going into the earning of income. The welfare of a nation can, therefore, scarcely be inferred from a measurement of national income as defined above.”

>If I babysit your kids and you pay me 1.000.000$, and you watch my kids and I pay you 1.000.000$, we just created 2.000.000$ in GDP.

This isn't the case with purchasing-power adjusted GDP, which is specifically adjusted to account for the actual purchasing power of people's money.

Would that still not in the above toy example lead to 0$ vs 2.000.000$/(some factor)?

Yes, but it's not going to have any meaningful impact on the overall gdp because it couldn't happen at scale (requires one party to have 1.000.000$ to spend in the first place).

But isn't this exactly what has been happening on a macro scale with the 'service economy'? We drew ever larger segments of people and activities into the world of financial transactions because of the massive amount of rentseeking money to be made in this environment. We doubled the amount of time the average family had to spend in salaried activity, and we passed start twice as now all activities that were previously selfserviced were also 'market' procured as no-one had time/energy left to take care of this after a long workday.

All money is fiat.

Yes, but the average Joe Bloe can't print money to pay a babysitter, only the government can.

I'm ignorant about economics, but that sounds wrong - if I offered my services as a babysitter, my contribution to GDP wouldn't be zero. If then I took the earnings from that job and hired a babysitter I would be at the same place.

What changed? You are now paying 250k$ or so in taxes, which benefits the government :)