The biggest problem I see with this, is getting the response back from the buyers. Obviously the people on BYC will help out, but if you sell some eggs on Ebay or other places, chances are the buyer will not take the time to give you the feedback your looking for. They just want their eggs.
It would be funny to see an eBay listing with part of the requirement for buying being that you have to send feedback on the hatch and arrival of the eggs haha!
Personally, I always go back and send a message to the person I got the eggs from- when I get the eggs with their condition, and then again when they hatch with how many hatched, how many developed, and how healthy the chicks are. If they are really good birds, I've gone back and left messages with them with pictures of the adults and stuff. But... that's probably the exception, not the rule sadly.