Chance upon this thread, and perhaps like to share my camera shopping in Seoul last month with you all.
Yes, the namdaemon area is the place and street for camera shopping. There are variety of new and used lenses and camera to offer. As a Nikon user, I bought 2 lenses on my last trip and it is mucher cheaper than in SG. For example, the Nikon 50mm f/1.4D at would cost about S$480 or more in SG. I bought it brand new at about S$370 ( with 1 year international warranty, and 2 year warranty under Nikon Korea). I later went to Nikon SG to endorsed my Korea recipt. Another example, I got my 14-24mm at S$2550, while SG is going at about S$2800. See the difference.

Languages is one key problem, but punching the calculator can solve that problem. Try not to use credit card (about 10% extra), bring hard KRW cash. You will not entitled or claim any VAT rebate at airport since most of the camera shops in namdaemon does not apply the VAT refund license with the government. Only expensive store apply VAT license, this is what I observe.

For Nikon shopper, please be careful to select the unit box with the blue Nikon Korea sticker. Those without could be a grey import set from Japan. You may have warranty problem when you come back. They are even cheaper, but I would not risk to buy consider the warranty.

Hopes this help. Happy shopping.