Buying an iPhone online (eBay)?

I need a new iPhone, an iPhone 6, same as what I have right now. I don't have an upgrade with Apple so it is very expensive. Some eBay ones say they are new and have sold hundreds. Most say the phones are unlocked, I'm not even sure what that means. Are they the same as buying them at an AT&T store like I normally do?

An unlocked phone means it is not tied to any carrier. (You can use any sim) In regards to your question about ebay, try using amazon instead as they are more realiable.