The Tax Authority from the Land Registry ( Oficina Liquidadora) could review the declared value of the property which appears on your Title Deed, this process is known as comprobacion de valores). The taxman could send you a Complementary Tax Liquidation (liquidacion provisional asking you to pay 7% transfer tax (Transmisiones Patrimoniales) on the difference between the value that you have declared on the deed and the value reviewed or market value as per their own valuation,.
This liquidation from the Tax Authorities could be appealed by means of a (Recurso de Reposicion) Reposition Appeal or by means of a Economic-Administrative Claim (Reclamacion Economico- Administrativa) in one month.Normally most of the time the Taxman review the declared value and issue the new value without a site visit, using general rules or coefficients, and just copy-pasting the precedent that they use. Being therefore quite common that the tax authorities review the value of the assets without complying with the legal criteria fixed by the courts precedents. This arguably leaves the citizens who are facing the proceedings unable to defend themselves in front of the taxman, opening up the possibility of having the penalty declared void.Therefore, if you receive a notification from the Taxman reviewing the value of a property and charging you a penalty, there may well be quite a lot chances to fight it with success if this is your case.