Seam splits are an easy fix.
There really is no guaranteed safe way to ship records, although some do it better than others. The larger and/or heavier the box, the more shipping costs, particularly distant locations like Japan. The best way to ship records, whether one or ten, is to sandwich the pile between two sheets of cardboard and wrap heavily with cellophane. Time consuming though, and a small shop will not have time or staff to do it, many of these are one man operations.
It is incumbent on the buyer to ask for the records to be shipped outside the sleeves to avoid seam splits. I have yet to encounter a seller who will not, buy the buyer must ask, as apparently many people seem to have some fetish about the record not being inside the sleeve. With used records, as there is no shrinkwrap, the record is highly mobile within the sleeve, and with movement in shipping - no matter what the box, or most packing, presents a sharp edge repeatedly striking the weak seam, often with force.
The physics of that is - sharp edge against a seam with force = seam splits. Inevitable.
