In general (based on the experience that I wrote about earlier in the week), preaching or lecturing is more likely to turn a pet store puppy purchaser away from you rather than convert them to your point of view. You have found, much as we have found, that it much more effective (although a slower process) to involve people in activities that illustrate good practice (e.g., observing examples of positive relationships with good breeders, helping at health clinics, volunteering (if only to serve coffee!!) at obedience seminars or watching a dog for you at a public education event). By doing this, they learn by example (rather than by lecture) and must reconcile in their own minds these examples with the inconsistencies of their own pet store experiences.
Much of the literature on persuasion would argue that you must first gain the respect and trust of the person (with regard to the topic at hand) BEFORE you can ever hope to persuade them to another point of view. [I learned this pretty fast when I had trouble convincing my father to take my advice in the area in which I do research and have a Ph.D.!! -- I quickly wised up and approached this at a more basic level getting him to eventually make the right decision.] Clearly, Cindy did this with her mother and has, as a result, created a convert. My advice on working with people who have already purchased a pet store dog is to help them be the best owner they could be to that pet store dog -- by all means, do not condemn them. In the process of helping them, you will provide enough positive counter examples to their pet store experience that when they are ready for another dog, you will likely be one of the first people that they seek for help. Nancy Melone, Ph.D. Mars, PA