After you're in the hobby awhile and buy trains from various out of state dealers you'll likely get to know the dealers who go the extra-mile and pack the train boxes in EXTRA-cushioned out boxes. They've likely learned, as have I, from experience that the shipping cartons from the importers are not enough to survive real-world handling & shipping. There's three dealers that I know of, and whom get the Lion's share of my business, who most of the time, use outer packing in addition to the shipping carton. Sometimes however, even extra cushioning doesn't help, but it certainly reduces the rate of damage.
From USPS - bullet #1 is key: