learn everything you possibly can about the breeds you are interested in because there may be some nasty surprises that you are better off knowing BEFORE purchasing your pup.
For instance, the size, health problems, the coat (if it needs regular grooming or if it sheds), if they prefer alot of company and cry when they are alone, are they better off as indoor or out door dogs etc etc
and the main thing.. what it the main purpose of the breed? Are they working breeds and will them not working cause behavioural problems?
Then I would probably inform them of the problems with buying from pet shops and non reputable breeders.