It's the oldest trick in the tourist scam book. You're breathless and tired, having just arrived in La Paz. You're wondering around the streets, hauling your backpack, trying to find a decent hotel to lay your weary head. And then some bloke comes up behind you and squirts mustard all over your backpack and then tries to wipe it off for you. You put down your bag while he helps you clean it, and then before you can say 'gracias', he nicks off down a dark alley laden with all your worldly possessions. Every hotel in La Paz has a noticeboard warning tourists about this scam, but by the time you read it, it's usually too late. Doh!