I couldn't find this until the last page before booking. The red bolded stuff is mine.
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Travel SkyMiles® Marketplace Terms and Conditions

1. Hotel and car rental rates are guaranteed only when redeemed at time of booking.
2. All bookings are final and non transferable. SkyMiles member who wish to cancel a reservation will forfeit all miles redeemed for that booking and may be accessed a change fee plus any additional supplier change fees.
3. Rules and fees for changing a booking vary depending upon each booking.
4. If changes are made to a booking, a set fee of $35 USD plus any supplier change fees may apply. Should a member make a change to a package booking (for example, a hotel and car rental) a set fee of $75 per reservation plus any supplier change fee may apply.
5. Change fees may be subject to the taxes due in connection with the provision of the hotel and/or car rental Award, including Sales Tax, and will be calculated, collected, and remitted by the actual vendor, or the intermediary providing booking and payment services for the actual vendor to you.
6. Rates may not include all taxes, service charges or other additional fees. Rental car companies require a credit card at the time you pick up the vehicle. Charges are billed at time of rental and subject to change.
7. Some hotels may have a Resort Fee that is not included in your package price. These fees will be payable directly to the hotel. In addition, your preferred bed size or type is based on availability and is not guaranteed.
8. Certain promotional tours, and non-refundable room categories and all optional activities (such as transfers, sight-seeing, theme park passes, and rail passes) do not allow any revisions once payment has been made.
9. Due to hotel supplier policies applicable to our preferred rates, traveler’s name may not be provided to the hotel property until 24 hours prior to your arrival. Please contact the toll-free number on your confirmation email directly for any support.
10. Car renters must be 25 years of age and have a valid driver’s license, major credit card and good driving record. Car rental suppliers reserve the right to deny rental due to past driving record.
11. Unused features of any booking are not refundable. The regulations and consequences of a "no show" by a guest may result in a total forfeiture of settlement and without credit due.
12. The distribution of a promotional hotel and/or car rental Award through the use of the SkyMiles Marketplace is intended to represent a payment on behalf of a SkyMiles Member for the direct transfer of the Award from the vendor (i.e., the hotel operator or the car rental company) or an intermediary providing booking and payment services with respect to the actual vendor to you. Neither Delta nor any affiliates or contractors of Delta shall (i) obtain possession, ownership, or other rights for hotel and/or car rental Awards or (ii) assume any obligations with respect to the provision of a hotel and/or car rental Award, other than the payment made on behalf of the SkyMiles Member.
13. For each hotel and/or car rental Award distribution, it is intended that the actual vendor, or the intermediary providing booking and payment services for the actual vendor to you, shall be responsible for reporting, collecting and remitting any and all applicable taxes due in connection with the provision of the hotel and/or car rental Award, including Sales Tax.
14. Where required by applicable law, if you are required to make a payment in connection with a request for a hotel and/or car rental Award, Sales Tax will be collected on the supplemental payment, determined based on the laws of the jurisdiction in which the hotel and/or car rental Award is delivered. Sales Tax will be calculated as a component part of the supplemental payment in a transaction involving partial payment by you to the actual vendor, or the intermediary providing booking and payment services for the actual vendor to you, in accordance with the paragraph above.

SkyMiles® Marketplace Terms and Conditions

1. Delta Air Lines, Inc. ("Delta") reserves the right to amend, suspend or terminate your access to the SkyMiles Marketplace at any time in its sole discretion.
2. SkyMiles Members must visit the SkyMiles Marketplace website to request an award of a gift certificate, merchandise or non-air travel (collectively "Awards").
3. You may request an Award under the SkyMiles Marketplace by redeeming the amount of miles required for the Award as provided on the SkyMiles Marketplace website. If you do not have the required number of miles for a full Award, but have at least the minimum number of miles indicated for the particular Award, you may still request the Award by redeeming miles for the Award and by making a supplemental payment with an accepted credit card when placing an order. The amount of the supplemental payment required will vary based on the number of miles applied to the Award.
4. Award requests are subject to SkyMiles account balance verification. Upon verification of the SkyMiles account balance and full payment of any required supplemental charges by an accepted credit card, the amount of miles you have redeemed for an Award will be subtracted from your SkyMiles account.
5. Only SkyMiles members 18 years of age or older may use the SkyMiles Marketplace to request an Award.
6. Awards available through the SkyMiles Marketplace may not be combined with or applied to other certificates, promotions or special offers, or special rate programs, including, but not limited to: upgrades, tour/travel packages, group, internet, convention/company meeting, senior rates, companion rates, third or fourth person rates, student or child rates, early bookings, value added price programs, repeat guest programs, or industry discounts.
7. No guarantees, warranties or representations of any kind, expressed or implied are made by Delta, or any affiliate or contractor of Delta with respect to the goods or services offered through the SkyMiles Marketplace; and neither Delta, nor any other affiliate or contractor of Delta shall be liable for any loss, expense, accident, injury or inconvenience that may arise in connection with the use of any Awards; or as a result of any defect in or failure of such Awards. Delta, its affiliates and contractors specifically disclaim any defect, in or failure of, such Awards and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose.
8. At any time, and without prior notice, Delta may change or terminate the SkyMiles Marketplace, change or terminate participating merchants, withdraw, limit, modify or cancel any Award, or change the number of miles required for any Award, even though such changes may affect the accrual or values of miles or Awards.
9. Miles are non-transferable and have no cash surrender value.
10. All transactions are final. There are no refunds, exchanges, replacements or conversions for currency, credit, other miles or awards for no-shows or unused portions of Awards.
11. The SkyMiles Marketplace and any offers or benefits therein are not available where prohibited by law. All federal, state, and local laws apply. Neither Delta nor any affiliate or contractor of Delta assumes any responsibility for any verbal or written representations made in conjunction with this program by participating merchants, suppliers, partners, any distributor and /or their agent(s), other than those included herein.
12. For United States federal, state, and local income tax purposes, any tax liability or obligation arising out of or attributable to the accrual or redemption of miles or the receipt of an Award shall be your sole responsibility.
13. You shall be responsible for any and all sales, use, excise and similar transaction-based tax ("Sales Tax") imposed on or arising with respect to any supplemental payment required to be made for an Award. Except as otherwise provided with respect to special shipping and handling charges, the supplemental payment required to be charged to a credit card for an Award and shown on the SkyMiles Marketplace website is inclusive of Sales Tax and will be separately stated in a written confirmation. You shall be liable for and indemnify and hold Delta and any affiliate or contractor Delta harmless for any Sales Tax later determined to be due resulting from the under-collection of such Sales Tax. You also agree to release Delta and any affiliate or contractor of Delta from liability arising from the over-collection of Sales Tax that is paid to the taxing authority.
14. All SkyMiles program rules apply. To review the rules, see SkyMiles Membership Guide & Program Rules.

Responsibility:

1. By use of the SkyMiles Marketplace website, you consent to be bound by all the terms and conditions as stated herein. You further signify agreement to these terms and conditions by submission of payment or redemption of miles for any transactions under this program.