Even after visiting 38-countries in my travel "career" I was surprised by the brazen nature of the scams in Istanbul. I can break them into three areas of concern:
The first is the Single Man Scam, (I won't go into great detail, either Goggle it or look on previous threads on here). There are many variations, and in just two days over last weekend I had approximately eight people approach me with this scam. They are as thick as mosquitoes in the Taksim Square and Sultanahmet areas. It will usually involve the person "thinking" you were Turkish or asking for a light - anything to get you stopped. Then, after some small talk, he knows of a great pub that was recommended by his hotel or a friend. I already knew about this scam from reading about it prior to arriving in Turkey and also restaurant workers also warned me. I knowingly let the first scam play out to see how far it would go, (it appears many work in pairs, possibly with a taxi driver involved). They will then not go to the agree upon area of the city, but to the prearranged pub. I ended the scam before I left a public location or lost any money. The other scams I ended before they could get far into their pitch.
The simple rule here, is DON'T stop or communicate with anyone on the street you don't previously know. Never follow a stranger's advice on pub.
The second scam is also an Istanbul-special - the cab driver scams. They include the money swtich, (yes, I admit I did fall for this one once) where they express confusion or are dismayed by the TRL presented for payment and want to switch the bills. Other scams include the broken meter game, taking you to the wrong location "that is near" where you want to go and "guess how I am going to get you there" - the wrong way. My favorite was the one where the driver wanted me to take me to a pub, "with hot Belarus and Ukraine women" and would not take no for an answer - going as far as to call the, "madam" to talk to me.
I have made it a habit of writing down, (so the driver sees me) his cab identification number, paying in small bills and having my Garmin on, so the driver knows I am watching his location from point A to B. Of the taxis I have taken here, I would say that maybe ten percent are honest.
The final scam, which is technically not a scam, is the outrageously priced night-club. Anytime anyone mentions a "night-club" run for the hills! Many times, the hawker will be completely honest - hoping you can't do basic math. For instance, he will admit that a drink you buy is 45TL, or more, per drink, ($20.45) for yourself and about 60TL ($27.27) for any women you might meet in the night club. By the way, normal places charge around 6TRL, ($2.72) to 10TRL, ($4.55).
Like I said, I was surprised by the number of scams that are in Istanbul - I have never seen this level of street crime in any other country.