If the egg is good, you'll be able to see the yolk right away if you put a light behind it. Fertile eggs don't always make it. Sometimes you'll see the yolk go soft and sink to the bottom of the case.
Often times, females will lay unfertile eggs. They are just empty cases.
Bad eggs can grow the typical 'fuss' and smell bad, but they don't always. I've seen them stay very clean. On the other side of that, I've seen good eggs 'fuss' and look very ugly with no impact on the pup inside.