tax rate on old tyres

Please clear full point On which amount paid "whole amount" or margin amount Because old tyre will be purchased from unregistered person which already paid tax on own Tyre purchase and sell them after use New Tyre basic price 24000/ +28% gst 6720/- total 30720/- After used these Tyre 1 or 2 month sell to Tyre dealer on amount 25000/- And dealer sell these Tyre to customers on Rs 25500/- Now clear gst tax on above tansection the profit is only 500/- on this dealing.