Never buy un-vaccinated chicks from anywhere. Several diseases are endemic to almost all poultry flocks whether you have problems with this or not. Marek's disease in particular is devastating. Salmonella is also pervasive. Chickens can be carriers without developing physical signs. Young chicks are absolutely susceptible. Vaccination will not necessarily prevent introduced chicks from getting a disease--but, if they do contract one they might survive. Vaccination builds immunity, but is not 100% defensive. Same as for humans. Marek's is horrible to experience, often with 100% morbidity. And it is almost impossible for the backyard poultry producer to eradicate it. Vaccinating chicks at a day old is our only hope to avoid this disease. Marek's is endemic in this country--even in commercial flocks. It ain't a pretty thing to endure.