The value of the supply of goods or services or both between distinct persons as specified in sub-section (4) and (5) of section 25 or where the supplier and recipient are related, other than where the supply is made through an agent, shall-
(a) be the open market value of such supply;
(b) if the open market value is not available, be the value of supply of goods or services of like kind and quality;
Provided that where the goods are intended for further supply as such by the recipient, the value shall, at the option of the supplier, be an amount equivalent to ninety percent of the price charged for the supply of goods of like kind and quality by the recipient to his customer not being a related person:
Provided further that where the recipient is eligible for full input tax credit, the value declared in the invoice shall be deemed to be the open market value of the goods or services.