It is not a big deal. I rarely get a broken egg in a nest because I am checking so often, but if an egg gets broken, you wipe as much as you can off of the other eggs immediately and set them aside for shipping. I absolutely never wash hatching eggs and will not buy from someone again if they wash their hatching eggs and ship them to me. On hatching eggs you can expect some soiling, dirt, blood, and feces. I take a dry sponge scrubber to all of my eggs before I ship them out, but I only lightly scrub off the loose stuff. Washing an egg can reduce its viability by removing the coating that helps keep bacteria out. The coating also helps keep the egg from drying out too quickly.
A breeder can reduce the dirtyness of the eggs by keeping clean nests, but it only goes so far. Here in Northern CA it has been raining since last fall and the ground is gross with mud. The girls will walk thru dirt or mud to get to their dry pen and when they lay the eggs in the nest sometime leave mud on the eggs.
Now seriously mud caked eggs is no excuse, because it is very easy to wipe off when you collect eggs. But a little bit of yolk is no big deal. It won't affect hatching, and shouldn't be a concern.
If someone want pristine sparkling eggs, they should not buy from me. LOL! I like there to be a little proof that I did not wash the eggs.
Lanae