I didn’t do due diligence on a client because I had worked with him before in another organisation. He didn’t pay his bill and it was the exact amount where it would have cost me as much to pursue it through the courts, as the total invoice. I had to write it off. When I did dig, it was a trail of fake addresses, dummy companies, and all-round fraudster. I filed a police report but not paying bills isn’t illegal apparently. Go figure. Now I am super vigilant.