Retail stores will sometimes offer "refreshed" items. For instance, if an iPod came in as faulty and the Geniuses didn't want to bother and just swapped it out, then realized later on that a factory/ system restore solved the issues, then that will be re-boxed and marked as "refreshed" or "open-box." It'll be cheaper and still warranted from date of purchase.
But you can bet that the receipt will be that much more important.
Note: These items aren't out for anyone to see, so you'd have to go and specifically ask an employee if they have any such products.