What I gather from that feedback, it's the buyer who has the genetic defect. That feedback reads like someone who didn't have a clue, botched the hatch with varying temps, etc. Then probably tried to weasel some free replacement eggs, and when the eggs weren't replaced, left spiteful feedback in the most damaging way that they could think of (genetics). The subsequent reply to the BYC'er who asked about the auctions supports my theory. JMHO.
All of the eggs that I got from her hatched at about 80% for shipped eggs, and all of my chicks from those eggs have eyes.
I think that as a general rule you have to side with the seller when it comes to feedback about shipped eggs. Just one glance through the "hatching eggs" section of BYC, and the questions and problems that you read there, shows anyone that there are a lot of clueless, inexperienced people trying to hatch shipped eggs. Many of these inexperienced, first time hatchers are the ones buying the
Ebay eggs, and when something goes wrong, automatically blame the sellers for sending them "infertile" eggs, even though the eggs spent 21 days with no water in the bator at 110 degrees in a shiny new bator that arrived on their doorstep the same day as the eggs.
I have nothing against people trying to learn hatching, we all had to start somewhere, but it sure looks like the excitement of it all gets to many, and they put the "cart before the horse".