You should never do this. You need a lawyer to guide you through the many pitfalls you may encounter, such as whether or not the property is fully legal. There are thousands of illegal properties for sale in Spain. If it is a resale you can check this yourself by looking at the Spanish land registry, or ‘catastro’ on ‘http://www.sedecatastro.gob.es/’ but you will need the Catastral Reference. A reputable lawyer will do this for you.