Rude or just mildy irritating?

I spend a half hour helping a family pick out books, chase their toddlers, read them a story, and then they purchase the books using an Amazon.com credit card. Yes, they're purchasing the books from me, the independent store, but with the Amazon card. I know the woman didn't mean anything by it. I know it wasn't done as some sort of odd intentional backhanded slap to the face. But really?
In my head I'm thinking, "I'm sorry, ma'am, but would you mind using another credit card? It sort of defeats the purpose of purchasing books at an independent bookstore when that sale is still going to support the empire threatening to put me out of business."
Instead, I smile and take her card, hand bookmarks to her two squabbling children, bag her books, and hold the door open for their overloaded stroller on their way out the door. Sigh.
Maybe we should start producing an Odyssey credit card.
Sometimes fighting against the man is harder than you think/want it to be, especially when the man appears to be everywhere. Even in your own bookstore.