Property Purchased Below Circle Rate

Dear Members,

My Client have purchased a flat for a Consideration of Rs.1,18,00,000/- and the Stamp Duty Valuation is Rs.1,45,00,000/- as the agreement was registered under the Circle. The Actual Price is below the Market Rate. I have searched few information in the Budget of 2013 & 2018 that some concession is given to the Purchaser but more clarity is required on the same.

Queries - 

1. Calculation of Amount that will be considered during Calculation of Tax under Income from Other Sources.

2. Judgement/ Cases to defend the purchaser in above certain cases/ situation

Suggestions are most welcomed. Thanks in advance