Burden of proof is on taxable person in respect of input tax credit :
If any person claims that he is eligible for input tax credit, the burden of proving such claim or claims shall lie on him – section 155 of CGST Act.
This is against the normal legal principle that burden of proof of any charge or allegation is on the person making such charge or allegation.
Further, in case of other demands, burden of proof is on department [though practically they do not prove anything and just confirm demand left and right]