Short answer: Don't.*
*Obviously, this advice is targeted at the casual carpetbuyer. Of course, if you know something about carpets and you are wealthy, you know where to go. There are plenty of reputable dealers in Istanbul who carry lovely and very expensive antique and new pieces. We're talking to people who visit Istanbul, who are not rich, don't know much about carpets and want a nice souvenir of their visit.
Go ahead, keep whining.
I want to buy a carpet when I visit Istanbul and don't want to get ripped off. Help meeeee.
OK, do it if you must, but there are some things to keep in mind.
You need to know what you're not buying. Very, very little that you will see in the Eighth Circle of Hell (known locally as the Grand Bazaar) is actually made in Turkey (the same goes for practically everything else in the GB). Labor is simply too expensive here to mass produce cheap carpets and kilims, so most of them come from Pakistan (nearly all cheap carpets are Baloch), Iran and, it may surprise you, China.
A dealer in Islamabad recently explained this China angle to us and a Turkish kilim designer confirmed it. The only thing Turkish about those carpets are the design. The wool comes from New Zealand or Australia and the dyes are probably some combination of melamine and spit. Apparently they are made in huge factories on looms lined up side-by-side with a foreman who calls out rhythmic weaving instructions, like the master on a slave ship (that is the analogy he used!). We would like to go to China to see this.
Mossmaniac and Carpetblogger spent the better part of the last two days in the Grand Bazaar (Carpet College!), in the belly of the beast as it were, trying to understand where all this crap comes from and how to identify it. We were lucky to find a dealer who was so clueless about his own stock and our poorly concealed mocking of it to not notice we were only looking at it so we could understand the nature of the odd colors and strange patterns that don't typically appear in Anatolian weaving and scritchy textures that feel like astroturf. China!
The rest of his stuff was cheap crap that's produced by the ton in Pakistan, with which we have more than a passing familiarity. That information had to be drug out of him. This experience discouraged us and made us hate the Grand Bazaar more than usual. Ask if the carpet you like is made in Pakistan or China or Iran. If you like it, you shoudn't care. But!
How can I tell if a carpetseller is lying? His lips are moving.
Do you have a dealer in Istanbul you recomnend? No.* Contrary to everything written above, it is possible to find older genuinely Turkish carpets or kilims in the greater Grand Bazaar area, if that's your bag. We suggest finding an older guy sitting in his shop drinking tea (most young touts have no idea what they're selling) and ask him to show you "something special." He'll take you into a back room, or open up a cupboard and you will feel like you found the Holy Grail. Your heart will beat faster, and you will feel faint. You will feel that the last six hours of hazing -- of listening to some maganda tell you that if the fringe is braided, it means a virigin wove the carpet and that cremesicle orange is a natural dye -- were simply the price of admission to carpet heaven. You will believe again in the zen of harmonious colors, tribal patterns and handspun wool.
Then the guy tells you that beautiful 70 year old yahyali is $6000 and you will laugh. You will say, "I heart Pakistan."
This is why Carpetblogger does not carpetshop in Istanbul. Cheap carpets are crappy and nice carpets are stupid expensive. We prefer to buy both in Islamabad these days.
"But Carpetblogger!" you plea, "I want to buy a carpet in Istanbul, not Islamabad." Ok, fine. What do we know about you and your taste? Don't listen to us. Do it. Buy something you like that reminds you of your nice visit here and makes you happy when you look at it on your bedroom floor. Don't believe one word you're told about its origin or quality, unless you're told "it was made by a Chinese slave in Guangzhou using spit and melamine dye," because that would be awesome and probably true. Don't pay a lot of money for it and bargain like, uh, a person who doesn't like to be ripped off by skeezy carpetdealers in the Grand Bazaar (you probably won't get better than 20% off, though). Be happy with your new carpetfriend and don't worry that you got ripped off because you totally did.
Coming soon! The Metaphysics of Textile Purchases: A Carpetblog Manifesto.