It is Disputed Issue. As GST Regime has similar provisions to what was existing before amendment in Budget 2015 which overruled case of Inter continental Consultants and Technocrats Ltd vs Union of India.
Section 15 read with rules provides for valuation of taxable supplies in GST. Coming on to specific portion relevant to reimbursements, clause (b) and (c) of sub-section 2 provides to include (i) Expenses incurred by recipient but which supplier was liable to pay
(ii) Incidental expenses and expenses for anything done by supplier in respect of supply of goods or services as the the part of valuation of supplies.
Definition of consideration contained in section 2 (31) of CGST Act is
(a) any payment made or to be made, whether in money or otherwise, in respect of, in response to, or for the inducement of, the supply of goods or services or both, whether by the recipient or by any other person but shall not include any subsidy given by the Central Government or a State Government;
(b) the monetary value of any act or forbearance, in respect of, in response to, or for the inducement of, the supply of goods or services or both, whether by the recipient or by any other person but shall not include any subsidy given by the Central Government or a State Government: Provided that a deposit given in respect of the supply of goods or services or both shall not be considered as payment made for such supply unless the supplier applies such deposit as consideration for the said supply.
Rule 7 of Valuation rules contain provisions of pure-agent which are similar to present provisions.