Well, my 2 cents on these sites.
DCDogfinders, the first puppies you see on their site are mixed breeds.
No reputable breeder breeds mixed breeds.
Here is a message board with some info on DC Dogdfinders.
DCDOGFINDERS.COM -- Glorified puppy mill?
Greenfield Puppies is a "front" operation for many, many puppy mills.
I would look for a known reputable breeder, not someone who appears to be acting like brokers. Look for a breeder who only sells their own pups, and not advertising for all and sundry.
They may look to have careful screening processes, however looks can be very deceiving.
I would check the breeder section on here and the Yorkies for sale section too.