The YTCA breeder list is the best place to find a breeder who is health testing and breeding Yorkies who will grow up to look and act like a Yorkie is supposed to.
Yorkshire Terrier Club of America About The Club
It is definitely "buyer beware" when shopping for a puppy on the internet. The internet is full of brokers, puppy mills, backyard breeders and scammers who will sell you a puppy who will grow up to barely resemble what a Yorkie is supposed to look like and have inherited problems like liver shunts, luxating patellas, etc.