I've only purchased
eBay eggs once; I received 14 (auction was for 12). One had a crack, so we set 13, and ALL 13 hatched!
My hatcher got an order from a very reputable (at least we thought) Marans breeder; they were supposed to be Blue Marans, and I think she ended up with maybe one blue; she had Cuckoo, Golden, and others that appear to be crossbred colors.
Regarding hatching eggs, I've been researching hatching them and from what I have learned, they are extremely difficult to hatch due to the dark coating. They also have VERY small pores (interestingly, making them immune from Salmonella poisoning), and the dark coating on top of them makes them dry down much slower, and often times, chicks drown. Some folks actually lightly sand the eggs before setting to remove some of the coating. Also, some folks hatch at a lower humidity than non-Marans eggs.
I know it's frustrating, but I sure hate to hear folks dissing
eBay sellers; as I said, my experience was absolutely awesome! I think you just need to be careful to do your research on the seller BEFORE bidding.