Bad debt deduction pursuant to Indiana Code Section 6-2.5-6-9, provides that a retail merchant may deduct from its gross retail income an amount equal to its receivables that: (1) resulted from retail transactions in which the retail merchant did not collect the state gross retail or use tax from the purchaser; (2) resulted from retail transactions on which the retail merchant has previously paid the state gross retail or use tax liability to the department; (3) were written off as an uncollectible debt for federal tax purposes during the particular reporting period. The Indiana Department of State Revenue own rule regarding Form ST-108 provides in relevant part that "if the vehicle is purchased from a registered Indiana motor vehicle dealer, the dealer must collect the tax and provide the purchaser a completed form ST-108 showing that the tax has been paid to him." IND. ADMIN. CODE tit. 45, r. 2.2-3-5(c). On the other hand, the Legislature has merely provided that "the state may not title a vehicle . . . unless the person obtaining the title or registration . . . presents proper evidence, prescribed by the department, showing that the state gross retail and use taxes imposed in respect to the vehicle . . . have been paid." IND. CODE 6-2.5-9-6(a)(1). Thus, whereas the plain language of Indiana Code Section 6-2.5-9-6(a)(1) merely requires proof that sales or use taxes have been remitted, the Department's rule requires additional proof that sales or use taxes have been collected by a registered auto dealer. See id. The Indiana Department of State Revenue "may not by its rules and regulations add to or detract from the law as enacted[.]" Johnson County Farm Bureau Co-op. Ass'n, Inc. v. Indiana Dep't of State Revenue, 568 N.E.2d 578, 587 (Ind. Tax Ct. 1991), aff'd by 585 N.E.2d 1336 (Ind. 1991). Accordingly, to the extent that the Department's rule requires more than a showing that sales or use taxes have been paid on the purchase price of a vehicle, the Department's rule is invalid. See Johnson County Farm Bureau Co-op, 568 N.E.2d at 587.