Maryland Code, Health-General § 21-1113

(1) May not assert as a defense that the person did not deal directly with the person on whose behalf the action is brought; and

(2) May prove, as a partial or complete defense against a damage claim, in order to avoid duplicative liability, that all or any part of an alleged overcharge ultimately was passed on to another person by a purchaser or seller in the chain of manufacture, production, or distribution who paid the alleged overcharge.