Finding a flat can be challenging in Barcelona. Especially finding a studio is difficult and you have to act fast. I went to see one studio apartment of 35 square meters in Central location beside good public transportation connections. The landlord was asking for a rent of 500 EUR including the electricity. Various people were ready to pay the rent so landlord was able to pick the person to who he wanted to rent the flat. Second potential flat was available for 580 EUR and as nobody had not yet decided to rent, I decided to make the decision right away and pay the reservation fee.
The rental agencies tend to charge 10 % yearly rent + VAT (21 %) from the tenants. Then you also need to pay 1 - 2 month rent as a deposit and the rent of the first month. Therefore you better be prepared with few thousand euros if you want to rent a flat. In Finland the landlords are paying the fee for the agencies to assist with flat rental. Normal rent contract is for 3 years which you can terminate after 6 months with one month notice period.
Since living here for over a year I have received almost every day a flyer to my mailbox from different housing agencies that they are ready to evaluate the price of my flat or help me to rent it out. If you want to rent a flat from certain neighborhood I suggest to a walk around and see the offered flats in the housing agencies of the neighborhood.