RTFM (or at least the website)
From apple.com
RETURN & REFUND POLICY
If you are not satisfied with your Apple purchase of a pre-built product, please call 1-800-676-2775 for a Return Material Authorization (RMA) request within 10 business days of the receipt of the product. If the item is returned unopened in the original box, we will exchange it or offer you a refund based on your original method of payment. The product must be returned to the Apple warehouse within 10 business days of the issuance of the RMA. All products must be packed in the original, unmarked packaging including any accessories, manuals, documentation and registration that shipped with the product. A 10% open box fee will be assessed on any opened hardware or accessory. If you purchased your order using an Apple Instant Loan or an Apple Business Lease, you may be asked to provide a major credit card (Visa, MasterCard, American Express, or Discover) for Apple to assess the 10% open box restocking fee.
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Mike