It is usually best if you can personally visit the place where the pup was bred and raised. We have traveled hundreds of miles to pick our pups. Buying online these days is very dangerous. Most online sellers are puppy mills and will have beautiful pictures and a lot of bunk about how many years they have been breeding and what experts and loving fur baby parents that they are...blah, blah, blah.
Most reputable breeders do have websites but they will not come up on a typical Google search. You need to know the name of the breeder. Go to
https://webapps.akc.org/club-search/#/conformation and look for a specialty Yorkshire Terrier club in your state. Of course you are not looking for a show dog but these breeders usually have pets available for sale much more reasonably than many puppy mills do. The reputable show/breeder cannot keep all the pups involved in a good breeding program so many are sold as pets. Depending on how large of a breeding program that they have some may have a wait list that is well worth getting on.
A reputable breeder will want to check you out to make sure you are able to provide a suitable home for their babies.
A Yorkshire Terrier club in your state or near your state will have people who can refer you to reputable breeders. Usually the referral person is listed on their website. You still need to do your own homework though by asking for pedigrees, referrals from customers, etc.
My experience has been that we have gotten a better price for a much better quality pet than what any puppy mill will give you.
You can recognize a puppy mill website in many ways. A puppy mill will not have any RECENT pictures of their stock at dog shows. They will not have any RECENT champion or grand champion sires or dams on their pedigrees. A good breeder will have a kennel name that is recognized by many other reputable breeders. The puppy mill may have some beautiful pictures of lovely dogs but usually they are professional photos that they did not even have done themselves. Stolen.
It can be a nasty business but there are some good people that breed dogs simply for the love and improvement of the breed. However, just because someone does show their dogs does not necessarily put a stamp of approval on the kennel. Everything needs you attention to detail. Talk to as many reputable breeders as possible to gain more knowledge of who you are dealing with.
Purebred dogs are genetically modified creatures. It is a very tricky business and in order to avoid genetic problems in the line the breeder must have a good grasp on the genetics of their breed. It is complicated and in order to breed purebreds well it takes a lot of time and dedication. That is why those pups may cost you a bit more, but if you have done your homework well it should be well worth your while.
As I said, many puppy mills will charge you as much or more for their pups as an established reputable breeder will. If that mill or their representative thinks that they have an uninformed buyer on their hands they will stick you with some poor little thing that could cause you a lot of heart break and a lot of medical bills besides.