Poa and income tax

Hi Experts,

        A land broker has POA from Person A to sell his land and when we checked to buy it, He is asking Broker commision + Income tax amount form the profit obtained from the sales as commision for the deal.

       Does a person who got POA to sell others property needs to pay tax for the profit obtained from selling that property?

       Should Broker register the POA in register office?

Thanks

Prabhu