The Commissioner, or any person authorized in writing by the Commissioner, is authorized to enter into an agreement in writing with any person relating to the liability of such person (or of another person for whom such person acts) with respect to any tax imposed under this chapter for any taxable period. Such agreement shall be final and conclusive, and, except upon a showing of fraud or malfeasance or misrepresentation of a material fact:

(1) The case shall not be reopened as to matters agreed upon or the agreement modified by any officer, employee or agent of this State; and

(2) In any suit, action or proceeding, such agreement, or any determination, assessment, collection, payment, abatement, refund or credit made in accordance therewith, shall not be annulled, modified, set aside or disregarded.

72 Del. Laws, c. 15, § ?17;