So, you have decided to sell your spanish property. It's not just a simple case of inviting agents in to acquire the necessary details in order to market your property.
There have been many changes to the law in Spain when it comes to the property market and this not only affects buyers, but sellers too.
In the first instance, contact agents of your choice and they will explain in detail all the necessary documents required. They are bound by law to hold certain documents on file for every property they are marketing. This includes yours too.
See the following details provided by Sunset Properties, here which informs you of all paperwork required for sale purposes.
Here's a brief outline of selling your property in spain
If you chose to sell your proprty via property agents. Negotiate the sales fee/commission and ideally have them all agree to the same figure!
Beware of some agents asking you to sign a document that refers to paying a commission for marketing your property whether it sells or not!
and Part 3 here