Value of supply of goods made or received through an agent.

Rule 29 of CGST Rules

The value of supply of goods between the principal and his agent shall-

a) the open market value of the goods being supplied or,

at the option of the supplier, be 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, where the goods are intended for further supply by the said recipient. 

b) where the value of a supply is not determinable under clause (a), the same shall be determined by the application of rule 30 or rule 31 in that order.