Other than the taxes mentioned in that section, you also need to bear in mind estate agent fees (often around 5% for international sales, less for local sales), lawyers / gestor fees, and banking charges.
Property in general is not the most liquid asset, and less so on the Spanish coast. The easiest properties to sell have the most demand, which means an attractive property in a consolidated area with good access and transport, walking distance to all the amenities. Also, crucially, you need to price to sell if you want to sell fast. So many owners have unrealistic expectations and spend years trying to sell. In my opinion it’s best to drop your price quickly to the market prices where sales take place, and get out fast. That’s on the case in areas where there is demand. If there is no demand, then price loses its effectiveness.