Just in my experience with chickens, I have hatched birds from dirtier eggs in the incubator. It MAY be putting bacteria into the incubator, but that is why I clean it. It's not worse in my opinion than all the little chicks pooping everywhere, at least this way they still have the natural protective coating on the egg. I will wipe off the dirt if possible sometimes, but there has been times where I couldn't. Mother hens never wipe the dirt off, and neither do they toss eggs after they've been a week or two old. If you think about how hens lay, and typically when they set the eggs are at least two-three weeks (sometimes more) old when they even begin setting. Not saying I'd sell eggs that old, but I do hatch eggs that old with great success. Out of the last batch (with dirty eggs, and some eggs were probably nearing two weeks or so) I hatched 14 out of 25 I think it was (may of been 23, or 24), the ones that didn't hatch I don't think were fertile yet due to the season being early here. Two other birds did end up being taken out of the shell- but I culled one and the other was a little weak so I guess it could be 16 instead of 14. The 14 birds though are going strong.
I wouldn't complain so much about how they arrived- but the hatch rates and service. Just because the eggs are dirty, doesn't necessarily mean that he doesn't take care of his birds. I try to make sure my birds are healthy, and safe, probably more so than others who wash their eggs (not saying anyone on this thread though.)
-Daniel
