[gwern]

There's at least one possible motive: they never got the money from the ads he was selling on their behalf, which were affiliate links. So he kept all the revenue from that. The longer they kept his ads enabled, the more ad revenue he could steal. Of course, when the mark finally figures it out, they can sue him for fraud... at least, if they still have money for lawyers. One way to distract them and stop them from checking the invoices or raising capital for lawyers is to drag out a fake investment. Seems to've worked. The startup went out of business and he kept all the money. Given how much they told him and were friendly with him, and as part of the due diligence, he probably knew pretty exactly how much they had left in the bank and were burning per month.