It's great that you are asking questions and looking around prior to buying a Yorkie.
Buying the breeder first is so important and can't be stressed enough!
You want to buy from a reputable, ethical breeder! Not a puppy mill, BYB or broker! It may seem cheap up front, but it will cost you in vet bills down the road. Not to mention you are lining the pockets of people who are living off the backs of their dogs!
I would suggest checking YTCA.org for reputable breeders in your area.
Personally, I wouldn't touch either site you have listed with a ten foot pole!
The first site as you mentioned breeds all kinds of mixes (which NO ethical breeder does), they let their dogs go home at 8-9 weeks and mention "teacups."
The 2nd site appears to be a broker site, run!
There are plenty of threads about Greenfield on YT if you search the name.
If you google both sites you listed you will find info on both of them being puppymills, brokers or both. That should be enough to not buy from them!