The problem with having another FTer broker this purchase for the ultimate buyer, is that the ultimate buyer loses out on some of the financial benefits that accrue to the one actually shelling out the cash or credit card.

These include
1) accumulation of credit card miles, or convertible points, for the purchase of the gift cards
2) 2% cash back on Executive membership purchases

There are also Costco branded credit cards which give cash back (up to 3%), but I don't know if gift cards are eligible for that rebate, or perhaps a lower one.

Economically, these benefits really do sweeten the deal for the buyer.