4. "Friendship" fraud.
A brilliant engineer friend of mine once hired his best friend's daughter to be his bookkeeper. He had known her as a kid. She was smart, hard-working and, because she was a single mother, she needed a sound income. As it turns out, she also felt mistreated by her father, felt her previous boss was out to get her, had problems at home, and needed this job to get out of debt. My friend is a great guy and a very trusting person. Within a year, the bookkeeper was the only one writing, signing and authorizing checks. She was running payroll and the only contact for the IRS.