No person shall be guilty under section 68a of this title if he establishes a guaranty received in good faith signed by and containing the name and address of the person residing in the United States by whom the wool product guaranteed was manufactured and/or from whom it was received, that said wool product is not misbranded under the provisions of this subchapter.

Said guaranty shall be either (1) a separate guaranty specifically designating the wool product guaranteed, in which case it may be on the invoice or other paper relating to said wool product; or (2) a continuing guaranty filed with the Commission applicable to all wool products handled by a guarantor in such form as the Commission by rules and regulations may prescribe.