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You can get warranty exchanges done at the Apple store no matter where you buy it.

However, if you decide you just want a different size or color it would need to go back to the place where you bought it.
 
apple will take back any of their products as long as they are under warranty.

Only if it is a warranty issue. Nothing more. They've refused returns from T-Mobile and Mac Mall, I've witnessed it first hand.
 
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