When you hear this story, you have two courses of action. If the owner is a real jerk and needs some comeuppance anyhow, buy his dog cheap. If he's a nice guy, but too inexperienced to know about growth phases, do the right thing and tell him the truth. Which is, this too will pass. If the dog truly was a natural in its first year, that dog will mature in its third year and come back with even greater ability.