Factory unlocked iPhones and gsn for craigslist?

I'm a noob at phones, and I've noticed that with cell phones there's a thing called gsn that you need to look for. Stolen phones would have bad esn. So my first question is: do factory unlocked phones have gsn?
my second question is, I've seen some pretty cheap factory unlocked iPhones on craigslist, some seem too good to be true, I'm scared that the phone would be fully functional when I use it, then when I bring it home it bricks on me. What should I look for in an iPhone when meeting up with someone from craigslist?

Added (1). MYBAD IT'S ESN

Iphone 4s has flickering screen and green wavy lines across it?

Had my iPhone about a month and in the last few days there's been green wavy lines across the screen at random points depending on which app i'm using, and there's a slight flicker at the bottom of the screen? For some reason this doesn't happen when it's charging though? Any idea how I can fix it?

Multiple wireless connections affecting ping?

So basically I struggle to reach a low ping when playing games which is irritating obviously. When browsing the internet I'm not to bothered.

I have 10MB/s connection which is pretty good so I know its not bandwidth being taken up. My PC is connected through wire to the router downstairs. Whenever I turn the wireless off my ping seems to be completely fine, minimal laag. But when its on and has about 6 connections from other devices (iPhones, iPad2, Macbooks, laptops) that people are using in the house the ping levels spikes even though the actual speeds are fine. Can anyone confirm that multiple wireless connections can cause the wired connections pings to spike or all other devices for that matter.

Also is it a router issue which needs replacing? Currently using a Sagemcom F@ST2504n which was supplied by Sky.

Why does everyone have an iPhone? - 1

I remember back in the day when they first came out, they weren't that common sight. Now it's like everyone has one. Aren't they expensive or did the cost go down since then? Is it because back then they were expensive but because of the contracts established with their provider they couldn't upgrade till they renewed? Or lack of priorities?

Which is better for me, 32gb or 64gb?

I'm getting an iPhone 5 tomorrow and i have about 850 songs and i download a lot of apps and i have some pics and videos but i don't have very many pics and videos

How to import pictures from an iPhone to a Lenovo laptop?

I have an iPhone 4 and a Lenovo laptop. I have nearly 7, 000 pictures on my phone and it's beginning to get irritating when messages pop up telling my I can't take a picture or I'm low on storage. I've had to delete a lot. I want to organize them and have them off my phone but somewhere else. So how do I put them on my laptop?