We had a workshop internally to decide on the triggers for different badges. If you look at the badge guide pdf they tend to be over double or triple the previous level's number. So our idea was the make each level exponentially harder to get (although not exactly). The level 4 badges should be much harder to get than the other levels, the jump should hopefully be big enough but we can always add higher levels in the future perhaps with some special colour variations!

Although for some badges we made the first one easier to get because we didn't think it was fair to have to do more to get it, such as Inventory Reviewer only requiring 1 review.