1) You can file a suit in state court for the state in which the customer is located. That is the only appropriate court under U.S. law. (As to whether you can sue him in Bulgaria under Bulgarian law, you'll need to check with a Bulgarian attorney.)2) The documents you describe are certainly helpful, but if the case goes to trial, you'd have to appear in the American court. Documents cannot be submitted on their own as the only evidence; there must be live witness testimony, in court, to authenticate them.