About used commercial vehicle

As per Notification 8/2018 CT (r)

Vehicle of Vat Regime Sold in GST Regime :
GST is applicable on Profit Margin (Sale-Puchase )

Vehicle Purchased & Sold in GST Regime :
If ITC claim , then GST is on transaction Value
If ITC is not claim , then GST is on Profit Margin (Sale - Purchase)

GST Rate 12 % & 18% is applicable as per CC engine of vehicle mentioned in Notification.
More then 1500 CC , leanth exceeding 4000 MM, GST is 18%
Else ,.. 12%