I've bought items on ebay before with warranties that are still honored by the store. I've got major deals, and you can trade it toward something for what the original price was (not what you paid).
But, I kinda bought what I liked and the warranty was icing on the cake on items 80% or more off retail. I had a particular ring (well a few) in mind and when I found it on ebay I snatched it (or them..hehe)!
I love how I don't have to worry about maintenance.
Don't forget about kay jewelers previously owned treasures site! It's kay jeweler's merchandise, you can opt for the warranty, and it's refurbs on what people have traded in.
I also did a google search for "pre owned jewelry" and found these sites. I still like ebay though.http://www.bravobride.comhttp://www.idonowidont.com/