Any agreement, whether written or oral, express or implied, for the payment of any money, compensation or thing of value as a fee for professional or other services rendered, as a brokerage commission, or as a “finder's” fee, or as any other kind of payment, which is dependent upon or contingent upon the approval of, or the making of, a loan by the authority, is hereby prohibited. At or prior to the closing of every loan the authority shall require proof of the absence of any violation of this rule.