You can always try your luck with costumes. SIM or Bella won't go down much, but hey, it's worth a try.
I will look at the costume, sigh, hmmmm, well..... Put it away, look at something else... Take it up again and hmmm some more. Finally ask sweetly: "I'm not sure... Can you make a special price fo me?"
If it's in a basar, haggle more. Example: A friend asked me to buy cheap hip scarves for her students.
"How much are these?"
"15 Lira." (or something like that)
"What???? ts ts ts... What is the price if I take more?"
"12 Lira."
"OK, tell you what: I will take 10 for 10 Lira each, OK?"
"OK."
So we put the scarves together.
"All this for 100 Lira, OK?"
"Yes"
Then I take another one, put in on top: "And this as a gift to me." (you need to be a bit flirty here)
He shakes head a little, smiles and says "OK".
It's always a good thing if you take several pieces. Makes it easier to ask for a discount.
But really, I did a whole tour comparing prices first. You CAN come back after walking away.
And yes, sometimes they will run after you and offer a better price themselves. This is your signal to go even lower - and in the end you will meet somewhere in the middle.
It's fun for a few days and starts to get on my nerves by the end of the week
Fortunately, in Istanbul there are enough regular shops where you can shop the Western way, so it's not a constant haggle from dust to dawn.
Have fun in Istanbul
MEISSOUN