I was talking to a rather wealthy friend of mine recently about theft. This guy was involved in the film industry in South America for decades, visiting primarily Brasil and Argentina during this time, spending lots of time. He should have known better...
He told me about three years ago he was wearing a $25,000 Rolex and was assaulted in the street. They were motochorros. The moto drove up, the guy on back grabbed his hand while twisting his arm and took the watch right off his wrist, leaving my friend in some amount of pain. The moto sped off.
Another friend of mine, who spent 20-some years here, recently left to return permanently to Australia. He was in the antiques business. Extremely smart, wise and well-studied in his field.
He went to to two different change houses he had always used, to recieve money he'd wired to himself here. He received a total of some 50,000 pesos. At one, he received 30K, at the other, 20K. In both, he put the money in his pockets while in the office of the guy he was receiving the money from. In the second, however, a secretary walked in while he was putting the 20K in his other pocket from the one that had the original amount.
He got into his truck and drove to his house. On exiting the truck, he was immediately held up at gun point. The thief reached directly into his pocket that contained the 20K and pulled out the roll. The thief didn't ask him for anything else, ran around the block and was never seen again.
The obvious suspicion was that the secretary called someone she knew to follow and rob my friend.
I won't say that anyone actually deserves to be robbed, but walking around the city, pretty much anywhere, with electronics and expensive jewelry isn't helping things. I knock on wood because I haven't yet been robbed, although every single one of my family has been. With the exception of my older sister-in-law, who was robbed of 1500 pesos from her purse just after she was paid (that being suspicious of someone who saw her get paid!), and my older brother-in-law who was robbed three times of amounts totaling to 150 pesos (living in Consititucion, he was robbed by the same gang three times leaving his "hotel" at 5:30 am to go to work), the thefts have involved cellphones, MP3 players and jewelry that was on display at some point.
My first friend was an idiot for wearing a $25K watch on the street. He recognizes that and only wears "cheap" watches now ($200-$500 US, as he says!).
My second friend took a risk of some random robbery while doing legitimate business but was screwed by dishonest people working in a change house. I have done the exact same thing many times as well, knowing there is a risk, but at least it's calculated.
You never know where it's coming from, but do the best you can to not be conspicuous. I walk around in shorts or sweat pants and t-shirts. I don't wear a watch or jewelry aside from a plain wedding band. I don't walk around with a camera photographing tourist things.