Meter rules are set nationally or by city, and in most places licensed taxis are legally required to run the meter for standard trips, with airport routes sometimes covered by official fixed fares instead. But legal requirement and street reality diverge in plenty of countries, so it pays to know the local norm before you land. In some cities refusing the meter is rare and taken seriously; in others it is a daily negotiation.
If a driver refuses the meter, the cleanest move is simply to get out and take the next cab, ideally from an official rank where drivers know they are observed. Agreeing a price before moving is the fallback where meters are genuinely not used. If you suspect a tampered meter, note the taxi number displayed on the license plate or inside the cab, take a photo of it, and pay only what seems reasonable.
Most cities have a taxi complaints hotline or a tourist police unit that handles exactly this, and drivers know a recorded complaint can cost them their license. Ride-hailing apps sidestep the whole issue by fixing the price upfront, which is one reason many travelers default to them.