Throughout the App, you will see listings with a small green dollar sign icon which indicates that the seller of that listing is offering a special discount. You can see the details of their sale or discount offer by looking at the listing or on their shop page directly. The little blue truck icon on a listing indicates a seller with a free shipping offer.
You can also search for sellers that are offering sales and discounts (as well as free shipping) from the people section of the PangoBooks app. Go to the Pango app home screen, scroll down, and tap the blue box that says "Search and Browse by Shop." On the next screen, you’ll see a row of sellers that are having a sale and a search bar to search for specific sellers. If you do a search for a seller or just tap “See All” on the row of sellers having a sale, you’ll now have the option to filter sellers by a few different parameters including whether or not they’re having a sale.