There was a thread running recently 'what do you do with your eggs?' I think, where this was discussed. It's a good job you can sell fertilised eggs because 90% of ours are. Presumably sight of the blastoderm (thanks for the extremely good info DBE) does not constitute discernable embryonic development, even though it is embryonic development and you can see it!
You need to be in the class 'farm gate sales' Suziequeue, otherwise it gets complicated. That was discussed in the same thread.