I didn't see any part of the page says it's only for new customer only.
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Getting your $25 rebate is easy: Just purchase $100 or more on Expedia.com, print out your purchase confirmation e-mail and mail it by January 15, 2002, along with the coupon above, to the address below. We will reimburse your credit card with the rebate after you have traveled. This offer is good for flights, Expedia Special Rate hotels and vacation packages. Please see the terms and conditions at the bottom of this screen for more information*.
* All coupons expire on January 15, 2002; coupons received after that date will not be honored. A $25 rebate is available to travelers who make their first qualifying purchase through the Expedia.com Web site for air, Expedia Special Rate hotels, or vacation package purchases over $100. Qualifying purchases must be made between 12:01 AM (PDT) August 24, 2001 and 11:59 PM (PDT) September 30, 2001. Traveler will receive a credit charge-back within 30 days after travel, once the above coupon and confirmation e-mail has been received by Expedia. A $25 rebate will be credited to the credit card provided at the time of qualifying reservation for any air, Expedia Special Rate hotel, or vacation package purchase over $100. Coupons cannot be combined, and are redeemable only once per booking per person. Travel must be booked by September 30, 2001. Travel must be completed by December 31, 2001. Please check the terms and conditions of your purchase for more information on reservation and cancellation policies. Any reservations that are made through Expedia.com and are subsequently canceled will not be eligible for a credit. If you do not receive your credit within 30 days after your trip, please call Expedia.com at 1 (800) EXPEDIA. Expedia is not responsible for misdirected mail. This offer is not valid for use in conjunction with any other promotional offer. Reservations are subject to availability. Rebate is void if coupon is duplicated or altered in any way. Coupons are not replaceable if lost, stolen, or destroyed, and are not redeemable for cash. Expedia is a registered Seller of Travel.
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