You walk into a retail shipping outlet and you pay 2-4 times as much, or more, than you pay if you box at home and print out your own labels. I just shipped a heavy piece of machining equipment across the country for $50. It would have been at least $200 to walk into a UPS store.
I get things that I bought arriving with ridiculous shipping charges on the label and I think "if this guy knew how to ship we could have split that extra $100". but you can’t tell the seller how to ship. You can, however, figure it out yourself.
Jerry