It looks like the retailer is essentially selling a gift card that gets automatically credited to the purchaser's Amazon account via the barcode they present. I

It looks like the retailer is essentially selling a gift card that gets automatically credited to the purchaser's Amazon account via the barcode they present. I suspect the retailer is getting a small cut of the sale just like they do with normal gift cards. Some of those giant gift card stands rent space from stores and I suspect Amazon has a similar arrangement for this.