There are 2 types of flat agencies in barcelona, 1 is the normal state agency (real estate agency) the same like in every country (with the only difference that you have to give the commission, not the owner), once you like the flat and take it you pay for it, but they show it to you for free.

The second one is a scam that is been running for a couple of years now, they tell you they will find you the cheapest flats in Barcelona and that you get it direct from the landlord (no commission), but in order for them to give you free lists for hundreds of flats every day until you find one, you have to pay them roughly a 160 euros, most of the ads for flats in the newspaper is from this types of agency, NEVER pay them they are all the same , I only met ONE person that actually found a flat thru them after 2 MONTH calling every day the WHOLE list. (all the advice we give is out personal opinion, if you think we are wrong please e mail us).