The typical Turkish taxi is a compact five-seat car which can seat two passengers in comfort, three passengers a bit tightly, and four passengers (one in the front seat) if the driver agrees.
Luggage space in the trunk/boot is limited, because in the largest cities, many taxis run on clean-burning LNG (liquefied natural gas). Much of the trunk space is taken up by a large LNG tank.
All taxis are required to have digital meters(taksimetre), and to run them. This doesn't mean they always do. If your driver doesn't start the taksimetre, or tries to haggle at the start of the trip instead of running it, just point to the meter emphatically and say Taksimetre! (TAHK-see-MEH-treh). It'll probably be cheaper.
(The exception is for inter-city trips, when a set fee—usually posted or printed somewhere—is the rule and ends up being cheaper.)
The starting fare as of 2021 is anywhere between 5-8 TL and goes up from there by each kilometre traveled.
Taxis may also travel between cities or from cities or airports to resort towns. For these longer trips of, say, 10 or 20 km (6 to 12 miles) or more, set rates may have been established. If not, you may want to haggle for an agreeable rate before you begin your journey.
As a foreigner, your driver may assume you'll give a tip, but you needn't unless the driver provides some special service, such as helping with lots of heavy luggage.
Some taxis are air-conditioned. Some have safety belts, and some even have safety belts in working condition, but don't bet on it.
A useful, cheaper alternative to the taxi in some situations is the local bus (shared taxi or bus).