Havent been to Caracass in a few years, but when I was going I was sternly warned repeatedly not to just take any cab from the airport. The ones you get from the desk insided the aiport were more expensive (as has been mentioned). There was a warning floating around the company I was working for that some ladrones were hijacking cabs on the way to the airport. They would then proceed to airport where they would hold up the drivers sign (with passengers name(s) on it) so that they could take them away and do bad things to them.