Section 9. The director or such person or persons he may designate from time to time may certify to the existence of any fact which may be a condition to the validity of any bond or note of any housing authority as defined in section one of chapter one hundred and twenty-one B or of the guaranty of the commonwealth on any such bond or note, and may certify that instruments and documents are true copies of instruments and documents on file with the department. The director shall file with the state secretary a written statement of any such designation and notice of any revocation thereof. Any person dealing with any such housing authority or with the department shall be entitled to rely on such certification as conclusive evidence of the matters therein certified.