There are a lot of Jansport backpacks sold over the internet and stores in the mall. The thing is, it is hard to know if the Jansport bags you are about to buy is authentic or not. There are several points that you must consider when buying a jansport backpack.
A jansport backpack has a lifetime warranty. When buying, always check the tags if it has a warranty card. All authentic backpacks have a lifetime warranty.
Jansport is also made of waterproof fabric which you may see as waxy on the inside. It is also lightweight. It also has a smooth feel in it. Try wearing the backpack first. If it feels funny when you wear it, do not buy it.
Lastly, always buy from trusted sellers and stores. Prevention is better that cure as they say.