There are a lot of misconceptions about fertilized eggs. Fertilized eggs do not taste different, do not have additional nutritional value, and do not have any different consistency. You can sell the eggs the same as unfertilized eggs. People will not be able to tell the difference unless they have very good eyes and know exactly what to look for. The only real difference is that if the eggs are incubated for 21 days they will produce chicks.
If a hen sets on the egg and incubates it for 24 hours, you could see some development. The solution is simple. Collect your eggs at least once a day. Some people collect them more often, especially if they are in a very hot climate or are concerned they will freeze during the winter, but I prefer to collect them in the late afternoon, around 5:00 p.m. All hens should have laid by then and I don't want eggs in the coop overnight. Eggs left overnight can attract predators, especially rats.
Growing up on the farm it was my job to collect the eggs once a day. We had roosters. As long as I collected them daily, we never had a problem with a fertilized egg starting to develop, even if a broody had been sitting on it all day.
Good luck!
