According to the Law of Agency, a supply manager acting as an agent makes decisions...

The Law of Agency establishes the legal relationship where an agent (in this case, the supply manager) acts on behalf of a principal (the organization). The supply manager, as an agent, has a fiduciary duty to act

in the best interests of the organization that employs them. This means making decisions and taking actions that align with the organization’s goals, policies, and best interests, rather than personal interests, professional norms, or overlapping interests of suppliers. References:

CIPS (Chartered Institute of Procurement & Supply) guidelines on the Law of Agency

"Supply Management" by David N. Burt, Sheila Petcavage, and Richard Pinkerton