Throughout the App, you will see listings with a small blue truck icon which indicates that the seller of that listing is offering free shipping. You can see the details of their free shipping offer by looking at the listing or on their shop page directly. The green dollar sign on a listing indicates a seller with a special discount offer.
You can also search for sellers that are offering free shipping (as well as sales and discounts) 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 offering free shipping and a search bar to search for specific sellers. If you do a search for a seller or just tap “See All” on any row of sellers, you’ll now have the option to filter sellers by a few different parameters including whether or not they’re offering free shipping.