(a) No licensed private investigator, watch, guard or patrol agency shall undertake to perform any services on behalf of a client unless such licensee shall have delivered to the client a written statement, signed by the licensee, which shall set forth the specific service or services to be performed and the charge or fee therefor. In the event any or all of the services are to be performed on an hourly or other periodic basis, the rate therefor shall be set forth and a limit fixed as to the number of such periodic units of such services that may be performed without any specific authorization from the client; such statement shall also acknowledge that the licensee shall not perform any services beyond such limit unless the client shall consent thereto in writing.

(b) Anything to the contrary of this Part notwithstanding, the statement provided for in subdivision (a) of this section shall not be required to be delivered if the client and the licensee have entered into an agreement in writing, setting forth the services to be rendered and the fee or charge therefor, except that if the agreement provides for or relates to services to be rendered on a periodic basis and no limit as to such services is established by the agreement and there is no express understanding by the client waiving the fixing of any such limit, the licensee shall deliver the statement provided for in subdivision (a) of this section, to the extent of setting forth a limit as to the number of periodic units to be performed, beyond which no such services shall be performed without the written consent of the client.

(c) The licensee shall obtain an acknowledgment in writing from the client of receipt of any statement of services or charges or executed agreement delivered, or maintain receipt or proof of delivery of such statement.