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.
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.