Never sell just to the Purchasing Department. Always know who the user of your product or service is and insist on having a working relationship with that person.
During each meeting with the Purchasing Department, be sure to ask at least one technically-oriented question about how your product/service is used. The objective is to get the PA (Purchasing Agent) to acknowledge they don’t know and ultimately refer you to a user or someone closer to the operations. This will more than likely begin a relationship you can use to demonstrate to the PA why your company is essential to their operations.
An alternate strategy would be to set up a “test” of some type that needs to be run to help you and the PA fully understand the return on investment of using your company. The test should involve some level of on-going measurement of performance that requires you to have contact with the operations and/or others who are using your product. By running a test, you will have contact with people other than the PA.
Plain and simple, if you work closely with Purchasing Departments and Purchasing Agents, strive to find ways to connect with the individuals who actually use your product.