Income tax filing

Dear All,

one of the my friend is running customer service center of nationalized bank in remote areas (Govt. Banks ---> Third Party--> customer service center) and he is getting commission on the basis of number of transaction customer does. When we go through his account flow the inflow and outflow is huge and the commision is bellow the taxable income. My query is that which form will be applicable in this case and how to avoind future uncertatinity?

Thanks in Advance