Depends on the hatchery. For some it's not all that rare, for others very. If their custoemr service is any good you should be able to email them pics of the chicks and get a yes or no conformation of any error from them.
Thsi is NOT against Estes. I've not ordered from them so I dont' know anythign about their quality, but ne aware the quality of a hatcheries breeding will affect the appearance of their birds. My aunts last order from a major hatchery got her 25 birds that were obvious crosses with the breed she wanted. She was mad and complainted with a very negative respose form the hatchery. She ended up treating the birds as meatiies instead of layers and is re-ordering from another hatchery. Sorry I don't have pics to share but it was soooo obvious it was sad.