This is something I found yesterday regarding Local Leves. In doing Local Craft Leves, you are given a set amount of Requested Materials to complete the order. You can, in fact, use your additional Material Attempts to gain additional skill, even if you've finished the order.
So for instance, you talk to the NPC, get your requested materials for that Local Leve, and you begin crafting. Two required, 4 Attempts offered. You finish the two required without fail, and still have two remaining attempts. Simply continue crafting for Skill & Experience points until you've used all of your attempts.
This doesn't not seem like an exploit, so you're simply utilizing the attempts given to you. If you failed the first two attempts, you require the remaining two, and you get skill for the failed attempts. So the way I see it, it's simply there for you to utilize. Initially I wasn't using the extra attempts, I was just using what was required and handing in the leve. The skill & xp gain can be significant and helpful, especially with raising crafting ranks.