The materiel administrator shall have had at least three years practical experience, in the ten years immediately preceding appointment, as an executive in a regularly organized purchasing department of some branch of government, municipal, state, or federal, or of some private business firm or corporation. He or she shall not be, at any time during his or her term of office, connected, interested, or otherwise concerned, directly or indirectly, with any person, partnership, limited liability company, firm, association, corporation, or other vendor, agent, or intermediary, from or through whom any purchases or contracts for purchases shall be made by him or her during his or her incumbency in office.