As part of the taxation procedure, the taxpayer has to comply with legal obligations to cooperate to determine the amount of the tax liability. Section 90 AO obliges the taxpayer in the preliminary investigation to disclose all facts relevant to taxation completely and truthfully and to provide all evidence known to him.
This also includes the provisions of Section 90 (3) AO for the documentation of transfer prices created with the StVergAbG. In particular, the duties to cooperate include keeping books and records (Sections 140 ff. AO), submitting tax returns (Sections 149 ff. AO) and participating in external audits (Section 200 AO).
In the case of matters with a foreign connection, the taxpayer is obliged to participate more closely (extended obligation to cooperate) in accordance with Section 90 II AO, as the tax authorities abroad only have limited options for ascertaining the facts of the matter. If the taxpayer does not meet his duty to cooperate, coercive measures are possible; the tax bases can be determined by way of an estimate (§ 162 II AO).