Hi! I’m the owner at http://www.catandravendesigns.com and we currently have two rules for shipping set up. The first is that if the customer’s order is $35 or more, they get free domestic shipping. The second is that orders weighing more than 1lb-40lbs are $8 flat rate. This is intended for orders less than $35 but too heavy to go first class and have to go USPS Flat Rate.
In general, these two work fine. But sometimes, even though an order is over $35 and less than 40lbs, the customer will be charged $8 in shipping. I can’t seem to locate any rhyme or reason as to why this happens only sometimes (maybe 1 order out of 75-100).