Trip to Mexico city questions

Re taxi: be sure that you get into a real, i.e. legal one. I know a British woman who's brother and an associate were sent to Mexico on a business trip. neither one had ever been out of the country. They arrived in Mexico city in the evening and got into what they thought was a cab. The guy drove them into a dark alley and relieved them, at gunpoint, of everything, including their clothes. He left them their shoes. For some reason, he's turned down offers to come visit in Zihua.