Often when packing up boxes to ship to Amazon you will have extra room. You can fill this with bubble wrap or air packs, but this is just a needless extra expense for the shipment. Some people already know to cut down the box to make it a tighter fit, but using a knife or razor to do it can weaken the box or even cut holes in it. The solution is the box resizer.
The box resizer creates a perforated line around each side if the box. Then you cut the corners so the sides can fold down along the perforated edge. You may still need some bubble wrap or air packs, but by cutting the box down you will decrease shipping costs and packing material expenses.