If in any case the Commissioner is satisfied that in consequence of the manner in which any vendor or class of vendors conducts his or their business, trade or occupation, difficulties, anomalies or incongruities have arisen or may arise in regard to the application of any of the provisions of this Act, the Commissioner may make an arrangement or give a direction as to-
a) the manner in which such provisions shall be applied; or
b) the calculation or payment of tax or the application of any rate of zero per cent or any exemption from tax provided in this Act,
in the case of such vendor or class of vendors or any person transacting with such vendor or class of vendors as appears to overcome such difficulties, anomalies or incongruity: Provided that such direction or arrangement shall not have the effect of substantially reducing or increasing the ultimate liability for tax levied under this Act.