Purchasing a quality purebred or crossbred dog is likely to cost you thousands of dollars; it’s an investment and should be approached the same way. 
If you’re considering a purebred dog or puppy, contact your national and state-based kennel clubs to obtain a list of registered breeders.
It’s a lot more difficult finding a reputable breeder of crossbred (designer) dogs as they are not recognised by National Kennel Clubs. My best advice is to do your research. Jump online and join dog discussion groups and forums, ask for referrals and speak to people who have previously purchased a puppy from the breeder.

Don’t be embarrassed to ask questions of the breeder. Reputable breeders will be happy to provide you with all the necessary information and will have a few questions to ask you too. 

Questions to Ask the Breeder

1. Was this litter planned? How many litters has mum had? Can I meet both parents of the puppy? 
2. Can I see the parents’ and puppy’s registered pedigree papers?  You need to make sure there are NO close relative matings, for example, brother to sister or grandfather to granddaughter.
3. Have both parents been genetically tested for breed purity and disorders common to the breed? Have both parents been hip and elbow x-rayed and scored? Remember this is an absolute non-negotiable in breeds prone to hip dysplasia and all giant breeds. Ask the breeder to show you the x-ray and hip-score reports. 
4. Have the puppies been raised inside the house or in the yard?  Make sure you see the area the puppies are being raised in. It should be a safe clean area with plenty of room for mum and puppies to exercise in. There should be enough room to allow toileting away from their eating space. There should also be things for the puppies to play with and chew, and plenty of environmental enrichment. 
6. Have the puppies been socialised with adults? Children? Other animals? The puppies should be friendly and play well with other dogs and people.
7. Has the puppy been registered, microchipped, wormed, vaccinated and received a thorough vet check? Ask the breeder to show you the documentation.
8. Will you provide me with all the information I need to know about caring for my puppy? Will you assist me with ongoing support? Reputable breeders should always provide ongoing support to the new owners of puppies they have bred.
9. Do you guarantee your puppies?  A good breeder should accept the return of puppies and dogs should health issues arise at any stage of their lives due to inherited disorders. They should also offer to take the puppy back within a specified time period if for a valid reason the puppy is unsuitable for your household. 
10. Do you have references? Ask for testimonials from existing and previous owners.