When you have a customer’s buyer who only calls you and gives you a verbal order, write all of the details in an email (price, quantity, who pays freight, taxable?, any surcharges applicable, handling charges, etc.) and then ask him to review and approve it with a “YES” or “OK” and return it to you. It is not a formal purchase order but will stand up in court if necessary since it is in writing and had the express approval and understanding of both parties.