The term AT is defined in GST Act in Section 2(6): “aggregate turnover” means the aggregate value of all taxable supplies (excluding the value of inward supplies on which tax is payable by a person on reverse charge basis), exempt supplies, exports of goods or services or both and inter-State supplies of persons having the same Permanent Account Number, to be computed on all India basis but excludes central tax, State tax, Union territory tax, integrated tax, and cess;
Now, what is value? Section 15 read with rules provide for the value. In case of the sale of second-hand cars, Value is margin, if positive. Thus, in this case, we will take the value for aggregate turnover. Here the value is margin.