Regarding this issue, I am a travel agent in Turkey and from experience I know that buying a ticket online with credit card if you are not the passenger, may be a quite a problem at the airport for the passenger. TK ground staff is not checking it every time but if you are checking in from the counter, they always ask to see the credit card. One of my clients bought a ticket for his father once because it was 5 TRL cheaper on the internet and had to drive to a city sales of office to show proof that he is the owner of the credit card.

But if you check-in online for the domestic flight, nobody checks the payment information. You just walk through security to the gate without any problem.