Lulu just emailed me to announce a sale in which the buyer gets a discount without putting in a coupon code -- just put the item in the shopping cart and it will show a discount. However, the discount is a "mystery." I don't know if this means it's random and different to each customer, or whether it's simply a deal where they don't say how much an across-the-board discount is. Or it might vary based on number of books. I have no idea.
However, if you haven't taken a look at the store recently, adventure your way over there (a couple of hexes at most!) and take a look.