I think the saddest part about this is that the average mom & dad and couple of kids don't set out to support BYBs or puppy mills when they decide to get a dog. I know I didn't know anything about them. My first Newf *would* have been from a BYB if the breeder hadn't lied to me and said the dam 'hemorrhaged and lost all the pups' (a lie). She gave us our deposit back.
We were fortunate enough to go to a dog show (the Detroit Kennel Club All-Breed Benched Dog Show) where we met with breeders of the three dog breeds were interested in and found our Max's breeder - and our Max- after waiting a bit. It gave us the added opportunity to look at other dogs while we were at the show, as well. But, of course, we fell in love with the gentle giants. (I confess "high energy" scared the crap out of me, when we were looking at goldens, and "sometimes skittish" when we were looking at Bernese).
But I can sure tell you, I would never have known where to find a reputable breeder......Keep in mind this was pre-Internet days, so often your only resort was to look in the newspaper want ads, the pet stores in the mall, or ask a vet - - if you had a vet.
The power of the Internet is wonderful. It's much easier to screen, contact, chat, etc, having computers!