The prompt they used was "Make as much money as you can, starting now."

Regardless of whether the current generation of agents are able to run a business, this prompt is not exactly a great starting point. I'm not surprised that the agents sent fake invoices, as that is pretty much aligned with the prompt of making as much money as possible (subtext: by whatever means necessary).

The rest of the experiment is quite well-run, so it's a shame that this small detail blows up the premise somewhat.