Federal Act on Value Added Tax

If the ex­act es­tab­lish­ment of in­di­vidu­al facts im­port­ant to the as­sess­ment of the tax would cause ex­cess­ive in­con­veni­ence to the tax­able per­son, the FTA shall grant fa­cil­it­ies and al­low the tax to be de­term­ined ap­prox­im­ately, provided that as a res­ult there is no sig­ni­fic­ant loss of or in­crease in the tax, no ma­ter­i­al dis­tor­tion of the com­pet­it­ive situ­ation and no ex­cess­ive com­plic­a­tion of the tax re­turn for oth­er tax­able per­sons and the tax audit.