Shipped eggs will always be a gamble. Okay call it a total CRAP SHOOT even. I've had from zero hatches to 100% and everything in between.
Shipping messes up eggs - whether it's heat, unpressurized cargo holds and moisture loss, postal gorillas, getting lost, or postal accidents.
Add seller's that YOU DO NOT know - and that's more risk.
Add breeds that are themselves fragile, or less fertile - for instance, seramas or the vaulted or rarer silkies and more risk.
You can eliminate some by dealing with breeders with great references. You do get better at compensating for shipping problems over time. At candling and catching and addressing air cell problems, seeing a more dehydrated egg, those kinds of things.
It is a gamble. It's a workable gamble in the long run. But you will get zeros and ones, and everything in between zero and 100 eventually. It does have a pretty high price tag on it - doesn't it? But it works out in the long run.