Each marketer shall ensure that its direct customers have a convenient mechanism for returning units to the marketer or to the responsible entity or to a destination specified in the unit management program covering those units. Except for direct sales to private consumers, each marketer shall provide written notice to its direct customers that each unit sold by the marketer is covered by a unit management program. Each marketer is responsible for units sold by it. The retailer location where units are collected under a unit management program may not constitute a facility as defined in § 7-101 of this article.