Do you think maybe you are getting old eggs? I sell eggs, but I keep myself to extremely high standards. I never ever will sell eggs that are over 7 days old and those are kept in a special fridge we have set up to hold a constant temp of 50 degrees. Most of the time the problems with hatch start out with the way they are stored prior to being shipped. Make sure your eggs you buy mail order are from a reliable source. I am so sorry you had such bad luck.
Are they from the same place? Maybe there's some spot from there to your place that x-rays or is stocked with gorillas, or has an exceptionally rough way of offloading packages. Sometimes even the best breeders/egg packers can't get their eggs to one specific area well, but won't know it because they either haven't shipped there or no one has complained (or they take the complaints wrong).