of this Article regarding the cost orientation of its prices, the burden of proof that charges are derived from costs, including a reasonable rate of return on investment, shall lie with the operator concerned. In verifying this obligation, the Agency may use cost accounting methods independent of those used by the network operator. The Agency may, by decision, require a network operator to provide full justification for its prices, and may, where appropriate, require prices to be adjusted. The burden of proof of this shall lie with the network operator obliged to meet this requirement. (6) Where the Agency imposes on the operator referred to in the first paragraph of this Article the obligation to use a cost accounting system in order to support price controls, it shall at the same time oblige the operator to make a description of the cost accounting system publicly available, showing at least the main categories under which costs are grouped and the rules used for the allocation of costs. Compliance with the cost accounting system shall be verified by a qualified auditor. A statement of compliance shall be published annually. Article 107 (obligation to regulate retail services) (1) The Agency may, in the decision referred to in the first paragraph of Article 101 of this Act, impose on a specified operator with significant market power on a specific retail market obligations relating to the regulation of retail services. (2) The Agency may only impose such obligations under this Article if, on the basis of the market analyses referred to in Article 100 of this Act, it establishes that a relevant market intended for end-users is insufficiently competitive and the obligations referred to in Articles 102 to 107 of this Act would not achieve the objectives it is seeking in the market. Obligations under this Article may include prohibitions on: 1. the charging of excessive prices; 2. the creation of barriers to market entry; 3. the restriction of competition by setting excessively low prices; 4. the giving of undue advantages to particular end-users; 5. the unreasonable bundling of particular services. (3) The Agency may, at the same time as imposing obligations under this Article, prescribe one of the following methods: 1. retail price capping; 2. the regulation of individual tariffs; 3. cost-oriented prices; 4. prices oriented towards those in comparable markets. (4) In meeting obligations under this Article relating to retail tariff regulation or other relevant retail controls, the operator referred to in the first paragraph of this Article must use the necessary and appropriate cost accounting systems laid down by the Agency in the decision referred to in the first paragraph of this Article. In doing so, the Agency may specify the format and accounting methodology to be used by such an operator. Compliance with the cost accounting system shall be verified by a qualified auditor, in accordance with the act governing auditing. The Agency shall publish a statement of compliance annually. Article 108 (functional separation) (1) Where the Agency establishes that the appropriate obligations referred to in Articles 102 and 106 of this Act have failed to achieve effective competition and that there are important and persisting problems and/or market failures identified in relation to the provision of