Even before I arrived, I found hotel websites that warned readers that some cab drivers would "take you for a ride," so they offered to meet you at the airport and take you to the hotel for about $45 to $60. A cab ride should cost about $30 from the airport to Sultanahmet.
Alternatively, a van service called Euro-Net charges reasonable fees. For three of us, our tab was about $27 nonstop to our hotel, and we could book the return at the same time.
When taking a cab, keep an eye on the meter. It should start at 2.00 YTL and advance 0.13 YTL every time it clicks.
Familiarize yourself with geography. If you can spot your destination on a map, you'll probably know whether you're being taken for a ride.
Be sure the cab driver knows where you're going. In my experience most drivers knew only the most common landmarks. Best to not only hand over the address but also to point it out on a map.
When checking into a hotel, confirm your room rate on arrival, even if you've received a confirmation e-mail. (Hotel rates often are quoted in euros, even though New Turkish Lira -- or YTL -- is the official currency.)
When you order a raki, the anise-flavored aperitif, in a restaurant, be precise about how much you want. If you simply order "a raki," you may get a double -- at double the price. Specify a single, if that's what you want.
When you're ordering appetizers, don't let the waiter goad you into ordering too much. Ask for what you want, and firmly set your boundaries.