One of the favorite blogs among reputable breeders is Ruffly Speaking by Joanna Kimball, I have her "Puppy Buyer Etiquette" link on my website and use it in my initial correspondence to puppy inquiries. Her explanation of why you do not choose your puppy is spot on.
I often have the same question of potential puppy homes and I explain (and often re-explain) that you should *not* expect to pick out your puppy (or their sex); a good breeder will have spent 8 or more weeks with the puppies before placing them, and they alone are in the best position to assess which puppy will do best in which environment – and often there are 5-8 families to accommodate. Doing what is best is the BREEDER's responsibility; similarly, you should want this kind of experience, expertise, and mentorship from your breeder.
Puppy Buyer Etiquette by Joanna Kimball
"PLEASE DO NOT EXPECT TO CHOOSE YOUR PUPPY. This one drives puppy buyers CRAZY. I know this, trust me. I have a lot of sympathy because I’ve been there. But the fact is that when you come into my house and look at the eight-week-old puppies and one comes up and tugs on your pant leg and you look at me, enraptured, and say “THIS IS IT! He chose ME,” I’ve been looking at people coming into the house all week, and every single time this same puppy has come up and tugged at them and every single one of them have said to me “THIS IS IT!”
What you are seeing is not reality. You are seeing the most outgoing puppy, or you’ve fallen in love with the one that has the most white, or the one that has a different look from the rest of the litter (when I had one blue girl puppy in a litter of black boys, every human that came in the house wanted her; when I had one black girl puppy in a litter of blue boys everyone kept talking about how much they loved HER), or the one that’s been (accidentally) featured the most in the pictures I’ve posted. Or, sometimes, you have a very good instinctive eye and you’re picking the puppy that’s the best put together of the litter. And that puppy, of course, is mine, and you’re going to have to pry him out of my cold dead hands.
My responsibility is not to make you happy. And that, dear friends, is why I am posting this now, and not when I have a bunch of actual puppy buyers around :D. But it’s the truth. My responsibility is to the BREED first. That’s why my first priority in placing puppies is the show owners, because they are the ones that will (if all goes well) use this dog to keep the breed going. It’s not that I like them better than I like you; it’s that I have to be extremely careful who I place with them so that they can make breeding decisions with the very best genetic material I can hand them. My second responsibility is to the PUPPY. I will place each puppy where I feel that it has the best chance of success and the optimal environment to thrive.
So while I do care, and I will try to take your preferences into account, do not expect to walk into my living room and put your hand in the box and pick whatever puppy you want. And do not expect to be given priority pick because you contacted me first; conversely, do not expect that because you came along late you somehow won’t get a good puppy. Sometimes the person who calls me when the puppies are seven and a half weeks old ends up with what I’d consider the “pick” for various reasons (sometimes because somebody called me up and said they’d gotten a puppy from someone else; see rule 4 above). I am going to try to do my absolute best to match puppies to owners as objectively as I can, not according to who called first.
ONCE YOU GET YOUR PUPPY, THERE WILL ONLY BE THAT PUPPY IN THE WHOLE WORLD."
Read the entire blog post here: http://rufflyspeaking.net/puppy-buyer-ettiquette/
