If the seller does not follow the steps in the link provided by Chris, you will have a problem. However, if he does, then you should be fine.
If the product is no longer covered by the warranty, then whatever problem comes up will be your financial responsibility. Note that Apple does not generally "repair" ipads - they may exchange it for a refurbished one.
Speaking of refurbished, you might be interested in checking out Apple's online refurbished store: you can save money and will have a regular 1 year warranty just like a new one. Their refurbs generally act and look like brand new. It would give you the warranty which you won't get with a used product.
Here is a link to all the refurbs iPads available right now:
http://www.apple.com/us-hed/shop/browse/home/specialdeals/ipad