Fertility is not a control on whether they get weepy or smelly. Fertile eggs can do that. If bacteria get inside and egg that is at 100 degrees F, it has a perfect environment to multiply, whether it is fertile or not.
The egg shell is porous so the developing chick can breathe. When the hen lays an egg, she puts a layer of something on it, called bloom that helps prevent bacteria from entering the egg. If that layer of bloom is washed off or if you scratch it off, then that additional protection is lost. That is still not necessarily a disaster. If the egg is in a sterile environment, bacteria cannot enter because there are none there to enter.
If the egg is dirty, then there may be bacteria there that can find their way inside the egg. I'm not saying that unless the egg is absolutely pristine that it will explode. Nothing is that clear cut. The bloom will help and just because there is some grime does not mean it will explode. I try to not set eggs that are very dirty, especially dirty with poop, but I don't obsess over it.
Sometimes water can be absorbed through that porous shell. When it goes in, that water can carry bacteria with it if bacteria are present. That is one reason to not refrigerate eggs before incubation. When you take them out of the refrigerator, moisture can condense on the egg and carry bacteria inside the egg. Again, it does not happen each and every time without fail. Some people refrigerate eggs for incubation and hardly ever, if ever, have this problem. It is just another risk they take. For some people, storing eggs for incubation in the warmer section of a refrigerator that is set at the high end of its operating range may be the best alternative.
So the best way to do it is to not scrape or wash the bloom off, do not incubate real dirty eggs, store them as best you can for before incubation, and sniff them occasionally. You should be able to smell them long before they explode if you remember to sniff.
Good luck!
