Many Marriott co-branded cardholders have now received a targeted offer to buy Marriott gift cards at 20% off, with a limit of $3,000. However, you must receive the email and use the code in the email to get the 20% discount.
This is actually a very nice deal, effectively making all Marriott hotels 20% off. Paying for a stay with gift cards is basically the same as paying cash: you can still earn elite nights as usual and enjoy elite benefits.