If the eBay one is new and comes with a warranty, it would be fine. When claiming warranty you contact Nintendo directly, not the place you bought it from. Just make sure the seller has a good rating and good reviews.
I've bought DS's and PSP's off ebay from Australian sellers with no problems Trillian.
The best thing to do is to check their feedback before buying from them and message them with your questions about warranty and whatever concerns you might have.
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