Whatever the Official Change Office offers Sedat at Zumrut always tops it, so ask before your change. Also, I heard the Change Office charges 4% to change Travellers Cheques.
We actually changed money with one of the cafe's in the Market, we had forgotten to bring out some Turkish money. We have used this cafe for about 7 years now and when the owner invited us in for our usual pancake breakfast we told him we were going home for our Lira as we only had Sterling. He immediately offered to change some money for us and asked us the exchange rate, we told him and handed over our Sterling and got Lira. We thought that was great service and so typical of some of the people locally we have become friends with.
Incidentally, found out last time that Zumrut means Emerald...Now Emerald Jewellers sounds good to me.