Reliability - purchasing iphone5 from a tech market in Seoul, South Korea?

I'm looking to buy an unlocked iphone 5 from a tech market (i believe this particular one is called TechnoMart?) in seoul. I'm just visiting the country and have only left few days. From where i'm from there's no apple store and the imported ones are very expensive. So i would like to buy one from seoul as cheap as possible. I tried buying one from an official reseller but they only sell locked iphones for 3year term contract. The other option is to buy unlocked one from the korean apple online store but the porblem is i don't have time for delivery as i'm leaving in 2 days. The only option i'm left with is the tech markets which are unathorized i believe.

So my question is:
1. Are these sellers reliable?
2. Do you know from where they get/import/manufacture these iphones?
3. I know iphones can be disassembled despite what apple store staff claim, so can these tech market sellers replace the genuine parts with lesser ones? Do they do that?
4. Why are they so cheap compared to apple online store. They are like 150$ cheaper.
5. Anything else i should know before buying one?
6. Again, are they reliable?

If anyone had experice please share. I know i should not be going through all this hassle for an overpriced product but i like it even though i can't really afford it. Please don't judge.

Any help is greatly appreciated!

Unfortunately tech markets (eg, Yongsan electronic market) is not necessarily the cheapest place to buy electronics anymore because of online sales. You should also look carefully with the warranty conditions.

I also heard that you will need to unlock your phone to be used outside Korea. Unlocking by Apple could cost $300. Check the carrier compatibility.

It's probably not worth the hassle. Just buy from Apple or a local eBay seller.