Be careful out there.....
Many items on ebay come with a warranty, but you need to be careful, as sometimes you dont get a receipt, and ebay auctions disapear after about 90 days.
If you dont have full contact details, and proof of purchase, then the warranty that was advertised is not worth the paper it was not printed on.
Its easy to offer a guarentee, but to be sure you can claim on it, you need to ensure that when you get the item you also know how to get in touch with them if it goes wrong.
Make sure you get a return address, telephone number and email address, you should also get a receipt, and the warranty on paper, or some other form you can use as proof. Without a copy of the original auction, you wont be able to prove the warrany existed in the first place.
Without contact details, you wont be able to return the item. Ebay user names can change, so you may not be able to find the seller. For your sake, make sure you get this information, or you may end up with a item you cant return for repairs or replacement.