She should have had early socialising with different people from a few weeks old. She should have had habituating to daily life, people, other dogs and so on. Unfortunately they have been caught in that common trap of believing they can’t take her out to mix until her vaccinations are finished.
In the most important weeks of her early life she wasn’t exposed to people. Or everyday things like vacuum cleaners and possibly other dogs. She has a lot to get used to. She is very scared when people visit, barking and backing away. On the left you can see her hanging back, her puppy curiosity trying to get the better of her sensitive wariness!
Darcy displays all the signs of a puppy who has not been kindly handled by a sufficient number of new people before she even leaves the breeder. One or more of the following factors could also contribute to the cause: being born to a fearful mother and maybe of a natural nervous disposition anyway, kept out of the way in another room or a shed for the first eight weeks of their life, possibly some inbreeding.
Using force, pushing him into scary situations he’s not ready for and even using a spray collar for when he barks at people on walks as ‘a friend said’, will have the very opposite effect to what they want him to grow up to be. A relaxed, friendly and confident adult dog.