well for anyone lurking, I thought I would let you know about this..
I purchased the "Like New" Amazon Warehouse deal. I was concerned about whether the warranty would be valid and I was getting an error checking on the Nintendo site so I called Nintendo Customer Service and they said the merchant had never reported a sale on that serial number so she would start my warranty service immediately. I was then able to confirm the device was under warranty from their website.
The 3ds itself WAS like new. I could barely find any remnants of it being used by another human. The only different was that instead of the factory seal on the outer box, there was scotch tape.
I then realize that the hinge was loose/wobbly between the top and bottom screen. I then googled about loose hinges and saw a ton of people complaining about this and a wide variety of responses varying from "every single one of them is like this" to "if the hinge is loose it is defective". I came to the assumption that most of these warehouse deals were returned due to the loose hinge issue.
I went to three stores trying to determine if the demo units also had loose hinges. Unfortunately, they all had metal braces keeping the hinge in a fixed position at the store.
I decided to order a 2nd one from Amazon, but this time I ordered a New one. It arrived, and it had the same hinge problem!
So at this point I am going to conclude that all 3DS's have this hinge issue and that if you are in the market for one, the Warehouse deals are just as good as new.
(BTW, the hinge isn't that bad, but if you play a game that requires motion of the DS, the top screen will wobble, which is kind of an annoyance)