Dear Sir,
No, you do not need to pay income tax on difference amount of auction price and govt valuation.
However, Properties under Bank Auctions are sold on “As is Where is & What is There is Basis” which implies Bank does not take any responsibility regarding Title of the property i.e. on encumbrance front, No liability of Bank. In the event of any legal dispute or any other claim on property, Bank does not indemnify the buyer from same. The complete responsibility of encumbrance rests with Buyer for auctioned properties.
It is always advisable to take help of Local Competent Professional Property Lawyer before participating in Bank Auctions as he can help you in understanding the rules and regulations. He can also help you to check Property Title and encumbrance on property (If any).