I'm ashamed to admit that this is the only scam that I've fallen for in my time in Barcelona (hence the image below of Homer). However, for my 9 years here, and considering the only thing the thief got away with was 500 pesetas and a cheque in my name (which was cancelled within the same 5 minutes it happened) then I think that's not bad going. Like most scams it's opportunism which caught me out.
I had just been paid from my old teaching job, and sat outside a cafe on Rambla Catalunya for a coffee with a friend on a terrace. As is commonplace with the terraces, you pay when the waiter brings you the drinks. This sounds like such an easy scam to fall for, but as we were deep in conversation it was difficult to realise it was happening. As I paid for the coffees, I left my wallet on the table, between our coffees. After a minute or so, an old tramp came over to our table with one of those free photo flip albums, but with postcards inside. He asked us (in Spanish) if we wanted to buy a postcard. Being able to speak a little Spanish, we shooed him away, rather uncomfortable with his presence. Obviously, he flashed the postcards over the table and lifted my wallet from under my nose, but as we were so deep in conversation, and eager for him to leave, this was the perfect distraction technique.
It was literally only seconds before I realised what had happened, and I didn't even comment to my friend, but leaped out of my seat and at a crossroads, took the busiest street - figuring that at least the thief would need an easy getaway. There are a few open shopping malls and a few shop entrances to hide in, but this savvy trickster was long gone. As I mentioned, I was fortunately able to cancel the cheque and get a replacement, but I felt (as I'm sure many do) so stupid at being duped so easily. Let this be a lesson to you all! Keep all valuables in sight - NOT on the chair next to you or on the floor in between your legs, but on your lap, or at least in full view. It's difficult to be vigilant at all times, but if you have any unsolicited help, or anyone offering anything for you to buy or charitable donations (I'm aware of a similar scam exploiting the real deaf aid workers offering key chains), then be alert!
For more information on Barcelona, see this Barcelona Guide.
I'd also like to mention Barcelona apartments for groups as a great alternative for hotels for group bookings, too.