Concerned about Getting Paid after Submitting an Invoice?

Use an escrow service. An escrow service is a licensed and regulated company that collects, holds, and sends a client’s money to a contractor according to instructions agreed on by both the client and contractor. Both parties agree to terms of the transaction, which includes a description of the service, price for each phase, the number of phases, number of days for the client's inspection, and who pays the escrow fee. Typically, once the client receives and approves the item from the contractor within an agreed time frame, the escrow service then sends the payment to the contractor. In this manner, you know that the money is available for the project, and that it will be released at pre-specified milestones.
 

Here are a few escrow service providers:
www.Escrow.com
www.iescrow.com
www.professionalescrow.com