If your backpack is of good quality, it will have reinforced stitching at key points such as the shoulder straps (top and bottom), zippers, and side pockets.  It will also have YKK or heavy-duty zippers, cushioned shoulder straps, and back mesh padding.  It will usually have pull tabs on the zippers and two-way zippers for each opening. Look for leather, canvas, or nylon for durability and longevity. A good quality backpack should last at least two years.