Fraud is an area severely under-appreciated and crucially under-funded. I think folks probably thought the banks/paypal solved the fraud problem but in reality as we know, it's pretty rampant everywhere. I think there's space for a few enormous anti-fraud companies on the scale of Symantec for example in different areas of security. It's an area I think that hasn't seen innovation in terms of the business model since McAfee and anti-virus first appeared.
Just look at the lending section of the forums and you will see how many clear examples of fraud there are. Granted the lending section does have many legitimate requests.