nothing to do with dirty tricks. Its make sure the tax man gets his taxes.
prices on websites mean little.
You have to prove that the value they have given the property is wrong. The taxman does not go an lookg at properties and value them, the calculation is based on location/m2/etc….
You can have to identical houses next to each other, 1 fully reformed to modern standards, wonderfull condition. The one next door has been rented to a family of 20 who have ruined the property, broken the pipes, crackes the windows, removed the kitchen and made a whole in the roof.
Hacienda would still given them the same values.