Exchange places could always offer whatever rates they liked. Under normal circumstances, the degree of closeness to the market rate would be determined by competition. I.e. you'd get excellent rates in the bigger cities (probably the very best being near the Grand Bazaar) and progressively worse in smaller towns and villages.
What you may find now is is a very large difference between buying and selling prices. I saw change offices in Istanbul buying dollars for seven lira, and selling at six liras to the dollar. Normally, the margins would be much tighter - eg 6.48 / 6.52 or something. But with the currency acting like a yoyo, that's only to be expected.
Edited: 5 years ago