Normally, market value and assessed value of a lot is indicated on the tax declaration for the purpose of paying the realty tax, and this assessment made by the local assessor's office where the lot is situated, is being changed from time to time. Market value of a lot indicated on the tax declaration generally is not being considered as the basis of the lot seller on how much he/she sells it to the public, but the current market value on the tax declarations, the selling price on deed of sale, and the BIR zonal value effective at the time of sale are being considered in the payment of the Capital Gains Tax and Documentary Stamp Tax, whichever is higher.
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I am not a lawyer but only sharing my opinion and knowledge through experience.