Ive only shipped crayfish and plants. I was scared too. The thought of shipping something always scared me. But after looking at guides, studying how others packaged and shipped things I tried it. Got all the materials, packaged it, and then shipped it off. Never had a problem yet.
Still have not tried fish, but I may try it someday. I know that with fish its a good idea to purge them for 2-3 days atleast. And smaller fish ship better than larger fish. Thats all I know.