Except as provided in subsection (c) of this section, a mortgage lender shall make a certificate under this section for every residential mortgage loan that the lender makes under a purchase commitment by the Administration with: the proceeds of purchase of a mortgage loan by the Administration; or the proceeds of a loan from the Administration. The certificate shall state that in the mortgage lender’s opinion, based on information given by the mortgagor and on the lender’s knowledge of the prevailing terms and standards of mortgage lending in the area, the mortgagor could not get a mortgage loan on the property in the unassisted private lending market. The Secretary may waive the requirement for the mortgage lender’s certificate for a residential mortgage loan to a homeowner: if the homeowner’s primary residence is located in a sustainable community, for the purchase or rehabilitation of the homeowner’s primary residence; for the refinancing of a residential mortgage loan of the homeowner if the loan was made by the Department or Administration; or for either of the purposes specified in § 4–237(a)(1)(v) of this subtitle.