Same thing happened to me when I bought my Speedy at the LV boutique in the Neiman Marcus in Tysons Corner.
I was all ready to pay with my bank card, and the dude tells me "Nope. Only cash, AMEX or NM charge". But he did tell me I could go to the concierge desk in the mall and get 2 Amex gift cards for the price of my bag and then buy them. That's what I ended up doing, but I definitely DO agree that NM has a stupid policy regarding payment. Although I do have an Amex now, I only use that for emergencies.
I was all ready to pay with my bank card, and the dude tells me "Nope. Only cash, AMEX or NM charge". But he did tell me I could go to the concierge desk in the mall and get 2 Amex gift cards for the price of my bag and then buy them. That's what I ended up doing, but I definitely DO agree that NM has a stupid policy regarding payment. Although I do have an Amex now, I only use that for emergencies.