Has anyone (non-Turkish speaker) purchased tickets over there with ease? If so, can they issue tickets with foreign departure and return (ie JFK-IST-JFK, probably so, but just double checking)? Does it cost a lot more than prices online? (given a fare bucket is available)

With the issue of booking Comfort multi-city itineraries and wanting to use miles for upgrades, I figure this will be the best way to do so during my next trip (for getting ticket for the following trip).