California Code, Probate Code - PROB § 4300

A third person shall accord an attorney-in-fact acting pursuant to the provisions of a power of attorney the same rights and privileges that would be accorded the principal if the principal were personally present and seeking to act. However, a third person is not required to honor the attorney-in-fact's authority or conduct business with the attorney-in-fact if the principal cannot require the third person to act or conduct business in the same circumstances.