[dopeboy]

Personal data point - in my six years of doing this (not fulltime), zero.

You can mitigate this risk in the following ways:

* Focus on taking in referrals; you're less likely to get hosed if you know a way back to them.

* Fixed contract + payment plan. As much as you can, negotiate one and have everyone sign it.

* Get clients in your geographic proximity. Spend a lot (say, 3 hours) of unbilled time with them in advance of closing a deal. This gives each party a chance to suss out the other. As with the first bullet point, you're less likely to get scammed because you probably know where they work.