I have never bought them but have seen posts of other people who have bought them. Some of the people that are experienced with them have said they fairly consistently only get 1/3 to 1/2 of the number of eggs they ordered. That is because they are shipped in moss and most people don't know what to look for. When only "half" of the eggs hatch, most people chalk it up to being how things go.
In a nutshell, either order twice as many as you really want or make a complaint after they arrive that you were shorted.