One of the biggest problems with getting a dog from somewhere other than reputable breeded, say a shelter or from someone selling an older dog, is you know nothing about it’s past. The dog could have had an abusive owner or even someone who loves dogs, but still believes in the negative reinforcement. If you bring that dog home, no matter how much you lean toward positive reinforcement, it remembers the past. I am not saying to not take on a rescue dog (a dog from a shelter). Without people willing to adopt one of these dogs, they would probably be euthanized.