You are not required to ship dead chicks back to a hatchery as "evidence," although if they are all DOA you can refuse the package.
If you choose to give them a little burial, it probably wouldn't hurt to take a picture of the shipping box with them in it, although I have never heard of a...
Just my opinion:
They overcharged you once or twice? Once can just happen anywhere, but twice seems a little much. Still, as 2Beauts pointed out, sometimes things do just seem to happen to one person. Have you ever had a day where everything goes wrong? I'm sure hatcheries dom too.
As to the...