I have been a veterinarian for 20 years, so I am quite picky when it comes to what I look for in a breeder. I was very impressed with Carlisle Cavaliers through the whole process and give them my full recommendation.
It is especially important with King Charles Cavalier Spaniels, since they have numerous health issues, to find a breeder that is working hard to improve the breed. Just having AKC registered puppies is not enough. It is crucial that a good breeder goes through the extra time, expense, and effort to have all their breeding adults OFA certified for multiple conditions. The Millers do this, and provide the certificates online and hard copies as well.
They welcomed us for multiple visits to their home, where we got to meet both of the puppy's parents as well as spend time with all the littermates. Not all breeders do this step either.
The videos on the website are a great feature, because they let you get a feel for each dog. Something that we noticed was that all the pups were very happy, people-oriented, not fearful or apprehensive, and lots of wagging tails. This tells you that they have had good socialization.
As a vet, I have seen my fair share of breeders who are not doing things right and put profit as their priority over the animals. However, I cannot speak highly enough of Carlisle Cavaliers as a breeder that is going above and beyond to be sure that they are putting out healthy, well-socialized dogs.
Dr. June Huff DVM (and Scout!)