First and most important is to find out from GameStop what their return policy is for a refurbished device (important for any retailer). Do not rely on the words of wisdom from the 16 year old checkout guy, knowledgeable as he may seem. Read their official policy and understand it. Verify it with a manager if there is something you don't understand. This is your responsibility.
Assuming you can return it to GameStop for certain reasons within a certain time period, refer to this post
http://forums.androidcentral.com/showthread.php?p=2411879 for my suggested inspection routine once you get it home. If you can't return it, perform as much of this inspection as possible in the store prior to buying it.
Next, make sure that the original warranty card (pamphlet, actually) is included with the N7. Also make sure that the serial number on the warranty card matches the N7. This is important. It would also be helpful, but not vital, if the original sales receipt from the initial purchase was provided, and if the N7 came in its original box, which makes it easier for shipping in case you need warranty service.
Despite this being a refurbished device, the Asus warranty likely still applies. If GameStop doesn't give you specific information about the validity of the Asus warranty, then the Asus warranty card has some specifically ambiguous information! (But keep in mind that regardless of what their warranty says, the laws with regard to warranty and consumer protection for your country or locality apply, if such laws give you more rights.) Here is a little bit of the Asus warranty:
This warranty applies only if the product was newly manufactured on the date of purchase.
Hmm, not sounding good for a refurb, but still ambiguous. Of course it was newly manufactured on the date of purchase, just not
your date of purchase. But later...
Enclose a copy of the completed Warranty card at the beginning of this Warranty, and a copy of Your Sales receipt/invoice from the seller. If you do not provide the receipt/invoice from the seller, your warranty period will be deemed to start from the manufacture date of the Product, based upon the serial number, rather than the date of purchase.
This is why I said that the original warranty card was important, but that the original (first time sold) receipt was helpful but not vital. This tells me you can get warranty service even if you bought it second hand, as long as it's within a year of the date of manufacture.
By the way, Google has nothing to do with this, because you aren't buying from Google, and they aren't the manufacturer or responsible for the warranty.
So in the end, I'd recommend going for it, as long as you understand and are comfortable with the possible pitfalls of going the refurb route.