So does the transaction happen under two vendors? I have a $250 Marriott card in my cart to meet the $25 back on $250 Amex Offer promo. The Amex Offer is saved to my card, and does not require going through a shopping portal. There is also a $30
Best Buy GC automatically added as part of a BB promo running on Marriott cards specifically. Would it be better to remove the BB GC and just buy the Marriott outright to trigger the Amex Offer? I pretty much never shop at BB for anything, so getting the $30 card but having that cancel out the Amex Offer wouldn't be a good deal.
Side note, the Best Buy Amex Offer does say no GCs - so wanted to confirm that someone used one in the past to buy gift cards and had it work.