I agree with BabyGirl Rosie: research the breeder's name on the internet and read the health guarantee very closely.
The houses and yards -- did you see these firsthand or just pictures on the internet? I would ask to visit and meet the pup's parents. Some bad breeders make everything look pretty on their websites to fool people looking for a puppy.
Ideally the puppies will be AKC registered and the breeder will only have Yorkies. If the breeder has several breeds, I recommend looking elsewhere.
Here are some more tips in the YT library:
http://www.yorkietalk.com/forums/bre...e-breeder.html
Best wishes in your search.