Iphone 5s!

Hello,

I wanted to ask about some stuff.

First : what is the difference between The ebay offers with " iphone 5s sprint" that are 400$ and those for 500$ ?
What is the difference between buying iphone 5s (spring , AT&T , T-mobile) from ebay and buying them from ebay?
If i bought any of them from ebay , which will work at egypt ( where i live) without the need of unlocking ?

Thanks in advance !