We should be able to send offers to people that have added a book to their shelves. I have lots of listings that get added to people's shelves, but not to their carts so I can't send them an offer unless I just change the price, which is time consuming and means I would have to continuously lower the prices of my books every time a new person adds them to the their shelves. eBay has this function of sending offers to people to like their listings, and I think Pango should have that function as well.