Agri Land Sale & Reporting Cash Component from Sale above Circle Rates in IT Returns

I am writing to seek advice regarding potential Income Tax related implications for sale of my agriculture land. I am planning to sell an agricultural land in a rural area. The Guideline (circle rates) value for the land is between Rs 30 Lakhs to Rs 33 Lakhs. The buyer wants to register the land through a Power of Attorney under-valuing the property under Section 47A (section in Tamil Nadu to under value and register a property) at a value of around Rs 12 Lakhs. I have refused this under valuation and I have asked for registration of the property at the actual value (which is above the guideline value) around Rs 50 Lakhs as I do not have the habit of handling cash as well as dealing in unaccounted incomes.

I have the following queries

If I register the property for Rs 30 lakhs (actual guideline value) and the receive the balance Rs 20 Lakhs in cash, Can I deposit the cash of Rs 20 Lakhs in the bank account and mention this cash in the IT Returns at the time of filing Income Tax Returns as cash received from sale of agri land and include it in the returns, If yes, what are the implications for me? I will not have Capital Gains as it meets the proper agri land criteria of distance from nearest municipality (and population criteria). Besides with indexation and indexed costs incurred by me it will actually be a capital loss for me, so I am okay to report the payment I have received in Cheque / Bank Transfers as well as Cash in my Income Tax returns.
What are the implications for me from an IT perspective if the buyer insists on undervaluing and registering the property?
What are the implications for me from an IT perspective if the land is transacted using a Power of attorney, as the buyer may carry out any legal & illegal activity which we will not have a control of and receive accounted & unaccounted incomes. What will be the implications for me and how do I protect myself? From an legal perspective I will be consulting a lawyer, but will appreciate suggestions from an Income Tax perspective to protect myself