Are you sure you did not misunderstand her when she said she could not guarantee fertility? It is true that she cannot, but that is why they ship a few extra eggs in case one or two were from hens that were not the roosters favorite.
When you have given up hope on the eggs, open them carefully and examine the yolks and air sacks. If the yolks are "scrambled" or the air sack broken, then it wasn't a fertillity issue, just the usual handling at the post office is hard on eggs.
Yes in every business there will be some that take advantage of their customers, and we should all tell each other about it when it happens.
But I'm not certain this is the seller's fault. It is probably not yours or or incubator's fault either. More like a function of the postal service (which is not designed to ship live animals or embryos, so no wonder things do not always work out well).
Bummer that we cannot come up with a better way to distribute eggs and chicks!