The Department may promulgate regulations to relieve authorized affixing agents from affixing stamps to packs of tobacco products to be sold and delivered to points outside the State for use outside the State, or to be sold to purchasers designated as exempt under § 5305(d) of this title for resale to authorized purchasers. However, all sales are presumed to be taxable and the burden is upon the person claiming an exemption to prove such person's right to the exemption.