I haven't had to ship any offspring yet as my creatures will not be breeding until this coming season, but what I was planning on was having a shipping AND handling charge all as one. Find out what it costs to overnight or same day the package, as well as the cost of packing/heating materials and add all of it as the shipping charge.
A person is interested in one of my snakes and would like it shipped. If the actual shipping cost is $30 and the packaging is around $12, I would quote them at $45 in order to ensure that I would not be losing money by accomodating them by shipping a live animal.
As long as they know that the charge is for the box, styro, heat, shipping etc... then I would assume that would be fine. That is how I felt when I had my animals originally shipped to me.
Good post man. As long as you're honest and up-front about your business practices, NO ONE can complain. Good on you.