Final answer:
Purchasing leadership, internal customers, and buyers should be involved in developing a firm's buyer appraisal system, as they provide the necessary insight to align the system with the firm's goals and operational needs.
Step-by-step explanation:
The individuals who should participate in developing your firm's buyer appraisal system are purchasing leadership, internal customers, and buyers. Although external customers provide valuable feedback on the products and services, they typically are not involved in the internal appraisal systems. Therefore, the correct answer is f. A, B, and D only. Involving these stakeholders ensures that the system aligns with the strategic goals of the purchasing department, meets the needs of users within the firm, and takes into account the practical insights of the buyers who have direct experience with suppliers and procurement processes.