I don't think I would buy something as expensive as a dslr on Ebay. Too risky, but then again you may like gambling
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A couple things to consider about warranty. One for the reason already listed that getting warranties honoured from an Ebay auction is not always possible.
The other is these cameras are very possibly ordered direct from overseas to cut down on price. I know some companies that will not honour warranties if you did not purchase the item from an authorised dealer. Some won't even service it after the warranty expires because it is what they call a 'grey import'. Could make it difficult down the track.