[tombrossman]

You can sit on one of the benches in the busier areas and easily spot the pickpockets and see them going in people's bags and backpacks and taking stuff. This isn't a rare occurrence and it does not take a practised eye to see. The pickpockets are always well dressed (usually very similar to the tourists). I like visiting BCN and I think it's a wonderful city, but it is completely infested with thieves targeting tourists to a degree that I have not seen in other European cities.

I'm surprised this is not common knowledge among people from there, maybe try 15-20 minutes people watching anywhere along Las Ramblas and see for yourself. Busy, sunny days with lots of people and police around are the best times to spot the thieves. You'll also frequently see tourist couples speaking to police reporting the robberies. You can watch the body language and gestures from a distance and it is very obvious.