This paper deals with the question of what taxable persons have to expect when they advocateanother legal conception than the fiscal authority. The first part discusses the official channels of thelawsuit and how these are organized in acts on fiscal offences. Further, the prohibition of the selfaccusation,dimensions and boundaries of the duty to collaborate, which can vary in intensity, will bedescribed. In addition to that, the tension between the duty to collaborate and the prohibition of theself-accusation will be mentioned.The second part will give an overview concerning the principle of legal certainty in criminal law forfiscal offenses. This gives a basic insight into the defensible legal conception apart from the criminallaw for fiscal offenses.Finally, the legal conception of the taxpayers concerning which facts they have to reveal to the fiscalauthority and in which dimension will be analyzed. Especially, it will be questioned in which cases alegal conception is reasonable, unreasonable, right or wrong.It will be presented which obligations a taxpayer needs to meet within the scope of a taxinvestigation and which violations of these duties can result in culpability or in an avoidance ofculpability. If a taxpayer can argue a justifiable misapprehension or is backed up by a reasonable legalconception, then culpability can be ruled out.Furthermore, an overview concerning the article of fidelity and faith and its applicability in thecriminal law for fiscal offenses will be given. In this context, it will be dealt with the question whenthe levy of taxes is inequitable for the taxpayer.