Local and global coexist in any tourist destination, and the challenge of tourism sustainability is what remains in the balance between these two dimensions. Social and consumer-generated media are changing how local and global are coming together in the local system. These media's effects are even more important in overtouristed places, where a significant imbalance between local and tourist development already exists. In this paper, the effects from foreigners' reviews in crowd-based ranking systems in overtouristed cities are investigated. Based on a case study of TripAdvisor's restaurant rankings in Venice, our findings suggest that foreigners' reviews systematically rate tourist experiences' quality higher than non-foreigners' reviews, and that their attitude significantly affects the ranking of these experiences. This discloses these systems' limited reliability in overtouristed cities when it comes to rank quality, as well as the potential risks deriving from their large and uncontrolled adoption. The study concludes that a governance system is needed that is more respectful and inclusive of these places' specific requirements.