Buying Yorkshire terrier puppies or puppies of any other breed online is risky because neither the puppies nor the person selling them may be as advertised. The risks are highest when going through websites that advertise puppies of multiple breeds or online sales sites such as Craigslist.
A puppy purchased online may not be the same one advertised in photographs, may not have its vaccinations, may be the product of a puppy mill or may not even be a purebred. If it isn't possible to visit a Yorkshire terrier breeder in person to see his puppies, the best bet is to visit the websites of breeders who are listed with the American Kennel Club or the Yorkshire Terrier Club of America. These breeders have agreed to abide by certain ethical standards and have reputations to maintain in the dog breeding world.