Don't be too quick to blame the post office. Hatching eggs are tricky because you don't know how many eggs were actually fertile until you've set them in the incubator for a while. Low hatch rates may be due to the eggs themselves. The post office may be innocent.
I have Black Javas, a heritage breed that needs a lot of work. My hatch rates are low if I count them from the day the eggs were set in the incubator. Maybe 25-30% are not fertile (no development when candled at 7-10 days). Others stop developing after that and don't make it into the hatcher. Of the fully developed eggs that make it into the hatcher, 20-30% don't make it out of the egg. So my overall hatch rate from start to finish is 25-40%, depending on the parents and the time of year and other factors. Low hatch rates are common in my breed. We java breeders are working to overcome that issue but it is only one of many issues in the breed that need improving.
Eggs I set in December and January had a much lower hatch rate (higher infertility) than the eggs I set in mid-late February from the same birds. The last batch I set barely fit in the incubator because I didn't cull as many non-developing eggs in the previous set as I had expected. (I set eggs every 7-10 days, so the incubator has two or three different sets of eggs in it at any given time. I remove eggs that are not developing as expected. Developed eggs get moved to a separate hatcher a few days before the hatch date.)
The only way to know if hatching eggs are fertile is to put them in an incubator and see what happens. The problem is that buyers of hatching eggs do not always understand this. It's one reason some breeders don't want to sell hatching eggs. It's hard to keep people happy.
