Does John have payment terms?
John provides an estimate with terms for each project. He also requires a purchase order from you. A purchase order can be as simple as letterhead or some other form of stationery that clearly shows John's name, your name and company, address and telephone number and that you have contracted John to work for you based on the estimate he has provided. With all new accounts, a deposit is required before work will start and the balance is due at the completion of each project.