In the end I was only one on the tour so I was pleasantly surprised when my guide, whose name was Roberto (not 100% sure) offered me that we do the tour anyway. He was professional and gave a lot of information about the other side of Barcelona, the quarter named Raval. If anyone wants to see the other side, I would recommend doing it with the guide.
Our guide Mariela was very professional and friendly. She showed us a different and interesting parts of Barcelona and provided us with a lot of information about the history of the city. It is a free walking tour although not really free which is completely understandable if you read the instructions when you are booking the tour so I adjusted my expectations. Nevertheless I was not disappointed although I would write some suggestions as a fellow tour guide myself. I would pay more attention to my group of everyone is there when I'm continuing to go further, give some time to take photos in some places and give more like fun facts, interesting stories and so on. Mariela gave us an access to web page where we can find a lot of recommendations which is extremely useful and very good idea with just scanning a barcode. She also had a lot of pictures to show us a parts of Barcelona through history which is always good idea and very interactive and useful