Taxis and Ubers are available in Istanbul. The general recommendation is to use either Uber or BiTaksi (BiTaksi may only be available to people with Turkish credit cards). Taxis scamming passengers is quite common. They will often charge more than the meter shows or not give change when paying with cash (taxis may be cash only). Even Uber drivers requesting more than the app rate is common (Ubers are taxis in Istanbul). If you’re being scammed, take a photo of their meter and any other way to document the scam and submit to Uber for reimbursement.
Car: At peak hours (8–9:30am, 5–8 pm) it is almost impossible to travel by car.