A Chic Outlet. There are many branded stores, the prices will certainly pleasantly surprise you.
If you are departing from Sabiha Airport, be sure to check in before departure.
Really an outlet, visited all the shopping malls in Istanbul. You can really buy a suitcase of things at a sooo low price if your size is! It is located on the outskirts of Istanbul, to get to the shopping center on its own, but I guarantee a wonderful shopping experience. As an example: I snatched off shirts for 2.5 lira, MAVI jeans for 33 lira, T-shirts for 10 lira!!!