When browsing books on PangoBooks you may notice icons on various listings.
The little blue truck icon indicates that the seller has a free shipping offer on their shop. This means if you buy over a certain value books from them, they will cover the shipping price to give you free shipping.
The small green dollar sign icon indicates that the seller has a special discount offer or sale going on. You can look at the individual listing or the seller shop page to see the specifics of their offer, such as a percentage off their inventory.