The vendor system allows you to unlock new items during battle that will then become available to buy in the shop. You get them for playing Co-op or Versus games. There are three vendor categories: Gear, Outfit and Equipment. On the vendor screen, you will see a list of items in each category. Choose the vendor category before each match and collect vendor points to unlock items in this category. Once you have unlocked an item, a new item from the same category will be randomly assigned to you.