When it comes to puppies, no one knows them better than the breeder who has been taking care of them and interacting with them since they were born.
However, if you were to find a dog through a shelter or rescue group, the workers at the group or shelter can probably give you a good idea of the dog's personality characteristics.
To help narrow your choice of which dog to pick, you can ask the breeder, shelter, or rescue worker the following questions: Do you have an idea of this dog's personality? Let the breeder know what type of dog you're interested in, for instance, if you want a mellower dog, or a more outgoing dog, the breeder will be able to point that particular personality out to you.
Is the dog comfortable around children? Most rescue groups or shelter workers will have some knowledge of a particular dog's demeanor when around other dogs or children.
In addition, breeders that have children can definitely give you a heads up on this one also.
I am really in love with this dog, is there any particular animal that I should not match her with? This is a question for people that have other pets in the household such as parrots, cats, rabbits, etc.
If you love a particular dog, the breeder, rescue, or shelter worker may be able to give the thumbs up for you to match your new dog with certain animals.
Has the dog ever been introduced to other animals? Just like humans, not all dogs get along with other animals or other dogs for that matter.
However, you can ask if there are any compatibility issues that you should be aware of.
You should spend as much time as possible talking to the breeder, shelter, or rescue worker so that they can match you with the right dog for your situation.
The more questions you ask the better position they'll be in to assist you with making the right decision.