Stamp tax on deeds of sale, conveyances of real property

Section 196 of the National Internal Revenue Code (NIRC) provides:
SEC. 196. Stamp tax on Deeds of Sale and Conveyances of Real Property. - On all conveyances, deeds, instruments, or writings, other than grants, patents or original certificates of adjudication issued by the Government, whereby any land, tenement, or other realty sold shall be granted, assigned, transferred or otherwise conveyed to the purchaser, or purchasers, or to any other person or persons designated by such purchaser or purchasers, there shall be collected a documentary stamp tax, at the rates herein below prescribed, based on the consideration contracted to be paid fqg^such realty or on its fair market value determined in accordance with Section 6(E) of this Code, whichever is higher: Provided, That when one of the contracting parties is the Government the tax herein imposed shall be based on the actual consideration: 
(a) When the consideration, or value received or contracted to be paid for such realty after making proper allowance of any encumbrance, does not exceed One thousand pesos (P1,000.00) fifteen pesos (P15.00). 
(b) For each additional One thousand Pesos (P1,000.00), or fractional part thereof in excess of One thousand pesos (P1,000.00) of such consideration or value, Fifteen pesos (P15.00).
When it appears that the amount of the documentary stamp tax payable hereunder has been reduced by an incorrect statement of the consideration in any conveyance, deed, instrument or writing subject to such tax the Commissioner, provincial or city Treasurer, or other revenue officer shall, from the assessment rolls or other reliable source of information, assess the property of its true market value and collect the proper tax thereon.