(a)Where the assessee incurs any expenditure in respect of which payment has been or is to be made to any person referred to in clause (b) of this sub-section, and the Assessing Officer is of opinion that such expenditure is excessive or unreasonable having regard to the fair market value of the goods, services or facilities for which the payment is made or the legitimate needs of the business or profession of the assessee or the benefit derived by or accruing to him therefrom, so much of the expenditure as is so considered by him to be excessive or unreasonable shall not be allowed as a deduction;