When one of your key criteria for selecting a dog is friendliness, the breeder or shelter employees can be very helpful. Having observed their dogs with a number of different people, they will be able to tell you which dogs are shy, which are outgoing, which are good with children, and which would prefer to live with grown-ups only.
When you do find a friendly dog, you must keep him in a secured area. Remember how he ran up to greet you when you first picked him out? He followed you all around the shelter or the breeder’s yard, wanting nothing more than a pat on the head or a belly rub. Although that was exactly what you were looking for, the dog doesn’t know he’s not supposed to do that with everyone he meets. He is just as likely to follow strangers who happen past your yard as he was to follow you home in the beginning.