Drivers who meet you before the exit quote $25–30 to Stone Town, then 'drop' to $20 like a favor. The same trip is US$15 at the rank — the official rate covers any Stone Town drop-off, full stop.
The most common upsell line at the airport: that the posted rate doesn't apply to tourists, or that your hotel is 'outside Stone Town'. There is no separate tourist tariff — the board is the price per vehicle.
Zanzibar taxis negotiate, not meter. Bolt coverage is reported in 2026 but sources wildly disagree on its fares (TZS 8,000–50,000 to town), so don't count on an app quote as backup leverage.
Drivers going the other way (town→airport) often quote above the posted arrival rate because there's no board in town to point at. Travelers' standard defense is to photograph the airport board on arrival day.