Had a great experience shopping here.. when it was open, lol.
I was helped by a friendly male and female SA, did not catch their names, but they were great. Luckily what I wanted was in stock.
They offer tax-free, but just make sure when you go to the airport to claim they actually accept it, as for some reason mine did not even though I know I received official global blue documents and I only found out when I went through security and all that to the actual redemption booth (FYI Istanbul airport does NOT make it easy to redeem tax-free shopping. You have to check in and visit 2 different counters and get in line with all the other tourists that thought it would be easy and actually show your items to them and then go through security and customs to redeem your refund at another counter and that's where you'll finally know what was accepted and what wasn't unless you inspect all your documents for stamps at the second counter.)
The hours online say they're open on Sundays, but they're not.
After shopping, stop off at the Cafe in the front lobby for a tea or coffee with a view :) read more