Total transparency...
I would add one more thing to this list...that is make sure your "virtual world" is totally transparent. I use a service called TransparentBusiness.com as it allows those who I contract with to track my progress on any and all tasks that have been assigned to me in real time. This application is seamless and can be used anywhere I go, or the employer in question goes. I also use this for my own team of outsourced employees so I too can keep tabs on them. This is a great way to end the threat of over-billing, which happens regardless of the size or stature of a company.