Certain countries- particularly in Central America and Europe, have a lot of taxis based scams, such as overpricing, taking overly long routes to run up the price or telling you they have a broken meter. Try to research what reasonable taxi fares are around the city or ask locals. Some cities also regulate prices and post them on their official website. To combat these types of scams, I always negotiate fairs before setting off. Just a general ‘it should be X price right?’ or ‘it should take X time to get to the destination?’. By non-confrontationally asserting that you’re aware of the general price or area, the taxi driver will be less inclined to try to scam you.