Except as otherwise provided by applicable federal or state law, if any nontaxable charges are combined with and not separately stated from taxable service charges on the customer bill or invoice of a service supplier, the combined charge is subject to tax unless the service supplier identifies, by reasonable and verifiable standards, the portions of the combined charge that are nontaxable and taxable through the service supplier's books and records kept in the regular course of business, and in accordance with generally accepted accounting principles, and not created and maintained for tax purposes. The service supplier has the burden of proving the proper apportionment of taxable and non- taxable charges. If the service supplier offers a combination of services that include taxable and non-taxable services or products, and the charges are separately stated, then for taxation purposes, the values assigned the taxable and nontaxable services or products shall be based on its books and records kept in the regular course of business and in accordance with generally accepted accounting principles, and not created and maintained for tax purposes. The service supplier has the burden of proving the proper valuation and apportionment of taxable and non-taxable charges.