Ok, after reviewing a couple dozen items between the eBay reseller, Best Buy and the Apple Store, I'm pretty sure the eBay reseller has to be an authorized Apple reseller.
Too many of the items they're selling are the same price as the Apple Store (if they weren't an authorized reseller, then they wouldn't be making any money).
It's possible that they could be working with an authorized reseller (but, why wouldn't the authorized reseller just setup an eBay store and cut these guys out then?)
My guess is, in the circumstance where the purchase date and warranty commencing didn't line up, it was a returned / open box item.
Heh...I sure wouldn't be buying an iPhone from these guys...they're pricing is absolutely nasty!!