I just used Iberia between Madrid and Málaga. I booked online and there was an additional charge of less than 10€ over the ticket price. I received the confirmations without problem. When I checked in, I just showed my passport although I was told that I might have to show the credit card as well. It was simple. I did take a printed version of my confirmation
There is price war going on right now between the airlines. Iberia has also discontinued its free food and drink on its shorter flights in order to offer lower prices. You can get stuff if but only if you pay and that includes water.
The lines at Spanair were enormous so give yourself time to check in!! I still prefer the train if I have time.
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sel