Need your earnest help regarding resell Property purchase

Kindly help as I am very new into this. Earnestly need your help in simplest form. I am going to purchase a resell property in Rajarhat. Property is 5 years old. The owner has not yet done the mutation. I think that means he has not given any property tax for the same. Now if I purchase what should I ask from the owner? As the mutation is not done, will it be done in my name now? Will I have to pay the pending tax for last 5 years or the owner will be paying that? What will be the pending tax along with fine and charges for mutation in my name? Kindly guide as I am very new into this.