I tried to hold my tongue for a long time, I recently disconnected myself from a friend who decided to breed her supposedly purebred but not papered Labs for money. I get it, people are more important than dogs, and if it were the choice between saving a humans life or a dogs life it's an obvious choice, but the difference is I cannot accept my friends putting animals through unnecessary bad experience or using them for selfish gain.
I'm not saying to disconnect yourself from this person, but just to look at the pros and cons, my 'friend' was bad for me and my sanity (there was more than just breeding dogs, that was just the last thing to top it off) so I made a choice for myself.
The only thing I would have to say is something along the lines of "whatever you do is your choice, not mine, but because of my passion for animals I have concerns I cannot help and I hope you will take the time to think about this and learn" possibly followed by a website link (if we are talking online) with reputable information regarding the issue.
I have to say though, I have not had success. The only way I have managed to help anyone or save a dog from an unfortunate living situation is actually getting my parents a dog before they went to a breeder. My parents are not puppy people and having raised a puppy when living with them I knew the first two years would be rough for them.
One of my brothers went to a backyard breeder, the other got a Czech GSD and is WAY too much for him to handle. My best friend got a 6 weeks old small breed puppy from a woman who flipped puppies. My mother in law bought a 'designer breed'. Even I years ago purchased from a BYB and my friends and family remind me about it, all I can say is yes I love my dog but I wouldn't go back to that breeder again. There's also then never ending list of things people do that I do not consider proper care of a pet, and the best I can do is recommend better methods, which does work better than just telling people what they are doing wrong.
If there were a perfect method to educating people on everything pets then there would be no more pet stores with live animals and retractable leashes would not be a thing.
The hardest part is just accepting you can't always make a difference or save an animal.