Except as provided in subsection (b) of this section, a person must have an appropriate license whenever the person acts as a manufacturer, retailer, storage warehouse, subwholesaler, vending machine operator, or wholesaler in the State. A person need not get a retailer license to act as a retailer at a vending stand operated under a trader’s license issued to Blind Industries and Services of Maryland. A license to act as a retailer is required for each place of business where a person acts as a retailer. A person licensed as a manufacturer, or person connected with the business of a licensed manufacturer or related by ownership, may not at the same time hold or have any financial interest in a wholesaler license or in any business of a wholesaler. A person licensed as a wholesaler, or person connected with the business of a licensed wholesaler or related by ownership, may not at the same time hold or have any financial interest in a manufacturer license or in any business of a manufacturer.