There are many exemptions for automobile dealers under the FLSA that are usually applicable to sales people therein. if your husband makes at least minimum wage depending on the compensation structure this pay practice may be legal. Please go over with a professional all the facts to see if there is something viable. Best of luck.
Please note by answering this question there is no attorney-client relationship formed. I am not your attorney. Nothing I said in this reply can or should be relied on. In order to rely on counsel's advise you must retain that attorney and receive representation or an official opinion letter. This is neither and meant to be for general informational purposes. Your case has specific nuances that goes beyond what you wrote and what I answered and you must speak directly with counsel to advise you of your rights. Please note I am only giving advice in the jurisdictions I am admitted (NJ, NY, PA). In any other jurisdiction I am discussing the law in general from an academic sense and not state specific rights. You should consult with a lawyer in your local jurisdiction.