Pets Online recommend that all prospective Kelpie owners buy their dogs from registered breeders even if it is slightly more of a hassle, as you won't know what you'll be getting yourself into with a backyard breeder.
When visiting a breeder's premises, you should ensure that they look after their dogs ethically and follow the RSPCA guidelines related to breeding. Ensuring they have the relevant documents for the dogs on their property will also be a good idea.
Finding reviews online of your chosen breeder will also help you to find out whether the breeder has bred healthy Australian Kelpie puppies in the past.
If you just want a Kelpie and aren't worried about getting a puppy, then consider adopting from a rescue organisation, as there are many adult dogs out there that need forever homes more than puppies do.