Years ago when in Lima, Peru I once saw a gang of lads surround an American backpacker and start jostling him. Then one of them slit the bottom out of his pack with a Stanley knife, all his things fell on the floor, then there was a free for all as the gang grabbed as much as they could before legging it.
Another scam was for someone to go up to a queue by a bus, they'd climb up onto the roof (South American buses nearly always had roof-racks) and start shouting for people to pass up their rucksacks. Unbeknownst to the people queuing they'd have a pick-up parked the other side of the bus. people would pass up their sack and the guy on top would pretend to put them in the rack but would actually pass them to his mate in the truck. As soon as they were rumbled the guy up top would jump into the truck and they'd be off. Interesting place Peru, I think it's a bit safer these days.