For real estate, a price below cost, the cadastral appraisal or the self-assessed value is not accepted, without prejudice to the market value being higher. Where price lists, databases or offers allow the market value to be determined, they must be consulted. In the deed the parties must declare, under oath, that the stated price is real and has not been the subject of private agreements for a different value, and that no sums were agreed or invoiced outside it. Without those declarations, income tax, occasional gain tax, registration tax and registration and notary fees are assessed on a base equal to four times the value stated in the deed, and the notary must report the irregularity; DIAN keeps its powers to determine the real value of the transaction (Tax Code, art. 90). If you have already signed, we review how to correct it and how to prove the value.