When I taught in a high school vet science program, I ordered hatching eggs every year. If you look on e-Bay, you will see that most sellers have a clearly stated policy that they are not responsible for the hatch rate and why. You might want to look there and see what they wrote. You might also include a website where they can get a "how to hatch" tutorial.
Not all of us customers are bad people. One time I got eggs shipped to me that were in an egg carton loose in a box. Most were broken. I politely suggested several better ways to pack and sent pictures of how to do them right. They replaced the eggs (packed properly) and thanked me- they were new to the whole thing. I have had great hatches and poor ones. The only time I felt it wasn't my fault or an act of God was when I got a bunch of rotten eggs and the seller had a lot of similar complaints. You may have to grow a thick skin and be grateful you were raised better than the nasty customer was.
Not all of us customers are bad people. One time I got eggs shipped to me that were in an egg carton loose in a box. Most were broken. I politely suggested several better ways to pack and sent pictures of how to do them right. They replaced the eggs (packed properly) and thanked me- they were new to the whole thing. I have had great hatches and poor ones. The only time I felt it wasn't my fault or an act of God was when I got a bunch of rotten eggs and the seller had a lot of similar complaints. You may have to grow a thick skin and be grateful you were raised better than the nasty customer was.