I think it would be hard to say if sick birds were sold, or if they developed possible Mareks after arriving and being exposed to it at home. Many of the big national hatcheries as well as the rare bird breeders, have shipped chicks who have eventually developed Mareks. The vaccine can be given at hatch, but the chicks may still not be protected until they are a minimum of 2 weeks old. These chicks were not vaccinated, so hard to know for sure.