Thought this snake looked cool and googled it. It landed me on a kingsnake.com care sheet where I saw this:
Many sunbeams snakes develop a condition that looks like blistering on their scales, this looks similar to a disease caused by excessive humidity-it is not. I am sure that many people, upon seeing this condition in sunbeams have thought that drying the snakes out would cure this problem, drying sunbeam snakes out kills them quickly. This is a bacterial infection exacerbated by stress and will disappear with correct antibiotic treatment and a humid environment.
So the stress of shipping could have caused this - meaning it didn't exist when it was shipped.