If you are looking for a way to respond in a positive way, that would be
something you can say...that you do offer discounts for multiple, volume purchases. It gets the message across without just saying "No."
BTW, I was in a business seminar for a very large company. They had brought in an international business "expert" and he advised that you should always ask for a discount in every negotiation. Of course, he was talking to a big business, but when asked, he said it should apply across the board because these days everyone is looking for business and should be willing to negotiate. See the post from GoddesssofJewelry above, who did a terrific job of negotiating and getting the sale. Congratulations, well done!
I also have a small, but existing group of sale items that they may not have checked out, so I would direct them there as another way to encourage a purchase.
Ladysprettys, thanks for mentioning that some shops do offer discounts if they are dealing with another Etsy shop. Good to be aware, especially if you are in a very competitive category.