In general it is better not to exchange much money before travelling to Turkey, as you can often get a better rate there. All cities have a large number of banks and ATM machines.
Banks are open from 9:00 a.m. to 4:00 p.m., Monday to Friday, with most of them closing between 12:30 and 1:30 p.m. for lunch. International banks HSBC and ING Bank are in Turkey, and many good Turkish banks also exist.
The easiest way to change money is at the döviz, a licensed money changer. Döviz bureaus are small, main-street premises; they are regulated and often give the best rates. Rates will be posted on boards (so compare if two or three döviz bureaus are near to each other) and the posted rate is what you get, with no extra commission.
US dollars, euros, and sterling are the most widely traded foreign currencies. Most hotels will change money, but they give a worse rate than the bank or döviz. Beware of money changers on the street. At best you may get a poor rate; at worst you may end up with counterfeit notes. You can check exchange rates here
Traveler’s checks are almost impossible to exchange and attract a high commission. Credit cards are widely accepted in shops and restaurants. Visa and Mastercard are the easiest to use; often shops are not equipped to process other credit cards, or debit cards.
Beware of fraud it is best not use your card in a small backstreet outfit. Many shops and hotels accept US dollars, euros and sterling.