I would leave negative feed back about the customer service, or lack there of, and the lack of prompt response to your concern. Unfortunately, the rest is luck of the draw. I have had some shipped eggs wrapped beautifully and hatched not a single bird and I've had them sent loose in a box of popcorn and had a very good hatch rate. It's all "buyer beware" on shipped eggs.
I dont' know how you can guarantee anything either.....definately not hatch rate. And I'd question a fertility guarantee as well. How do they know each egg was fertile? What if the rooster forgot a hen or there are too many hens per roo. Seems to be shooting yourself in the foot to make a promise like that. Air sacs detatch and egg cells die in transit. It may have been fertile when it left the seller, but depending on age, distance, handling - all that contributes to the killing of the cell.