Second hand car dealer - income tax

Hi, My Client is dealing in Second Hand Car Purchase and Sale. He purchases the car by making payment from bank and after few days he sells it to customer by receiving the payment in bank account with his profit margin. As per Income Tax, how do we need to report the Sale and Purchase Transactions? - Do we need to directly disclose his Commission as Revenue or Gross amount of Sale and Purchase needs to be disclosed in P&L Account? Kindly help to solve this query. Thanks..