I talked to a guy last night with a great story about a friend of his who got a little drunk, took a pretty hard dive and broke a few bones. As he lay there all but immobile, a taxi driver came up and asked if he wanted to go to a hospital. The guy said he didn't, that an ambulance had already been called. The cab driver shrugged, then reached for the guy's wallet and ran off with it as the poor slob lay helpless on the ground.
It's a secondhand story, but it rings true because the cab driver was honest and helpful to a point but, come on, he was presented with a once-in-a-lifetime opportunity to help himself to a free wallet.
There are quite a few stories about dodgy cab drivers and robberies. You definitely need to be careful. Still, I don't take cabs very often, but I have twice had cab drivers round down the fare. On another occasion, the cab driver knocked a couple pesos off the total because I asked him to take me to a store that he hadn't known about and, as he said, discovering that store was worth something.
Maybe they could only afford this generosity because their wallet-snatching gigs were going so well for them.