It's a little-known market, but it really exists, and it is expanding: sales and rentals of casas okupadas. This is the term used in Spain for homes lying empty after the original residents were evicted for defaulting on their mortgage, or because they were bought by a bank and never inhabited, or even because it was subsidized housing that had not yet been assigned to a low-income family; in any case, all these homes end up being occupied illegally by squatters, known in Spain as "okupas" (squatters).
But now, squatters are not just those who pull down a door and move in by themselves. Instead, organized gangs in Madrid are taking over these vacant properties first, and offering to either sell or rent them to would-be squatters. "Purchasing" one of these apartments costs anywhere between 1,000 and 2,000 euros, while renting is more expensive in the long run, since the gangs ask for 200 to 400 euros a month.
In exchange, they guarantee customers immediate access to the home as well as free electricity, gas and water services, and some even offer free heating (typically, this is courtesy of other building residents who see their own bills rise mysteriously). The new residents don't even have to pay building maintenance fees. Their situation is guaranteed until a court rules to have them evicted. But months could elapse before that occurs, if not years. The Regional Federation of Neighborhood Associations (FRAMV) says that this is a growing trend, especially in the residential areas south of the capital.
Mortgage and rent defaults caused by the economic crisis have meant that many people were evicted and left without their homes, leading to a notable increase of vacant apartments. This in turn has led to a spike in illegal occupation: homeless people are taking advantage of the "availability" of these homes, but how to know which properties are really uninhabited, to avoid additional trouble? Organized gangs can provide the answer to that, in exchange for a certain amount of money. These criminal organizations do not hold sway over an entire region; instead, they are small groups who wield their power at the neighborhood level. They have their rates: 200 to 500 euros to unlock an empty home; 200 to 400 euros to rent it out, and 1,000 to 2,000 euros to "purchase" one.
In Madrid, these groups operate mostly in the southern districts of Carabanchel, Villaverde, Usera, Arganzuela and Puente de Vallecas, according to FRAVM. These lower-income areas see the largest concentrations of unoccupied homes and subsidized housing in the city. According to 2011 figures from the National Statistics Institute, there are around 306,000 empty homes in the capital. But there is no data on the number of housing units which are illegally occupied.