One of the most interesting things I’ve ever learned is that website shipping charges are nearly always a shot in the dark. I use a fulfillment service (like many companies these days) and have called the owner about 10 times to re-explain this to me since it’s so baffling to me.
Like playing the lottery, there are strategized guessing systems that every business uses to in hopes that they’ll come on top at the end of the day. For a checkout cart to generate an accurate number based on box size, weight, destination city + residential/business, rural/metro in both ground, expedited and USPS would be wildly complicated. So, you narrow down that factors and just guess. I love that. I guess that’s a pretty accurate description of most businesses in general.