I have a good friend who loves German Shepherds. I too, admire the breed. But I know far less about that breed than my own chosen Rottweilers. When she asked me where to start on her quest for the right breeder, a few things came to mind.
Read the books. Read all of the books. Then read some more. Read the websites. Read all of the websites. And when you're done reading all of those, read some more.
Get everyone's perspectives on everything. And then begin to draw your own conclusions. That way, when you begin to meet breeders you have a good idea of what might seem fishy to you, and what might register with you as a very good sign.
Now, start visiting the breeders who didn't raise any red flags for you; the breeders whose content made you feel confident and comfortable. You're not just purchasing a puppy, you're purchasing that breeder's decisions, their research, their nutrition, their socializing and so much more that they do or DO NOT put into your puppy.
Exchange emails and phone calls to help you narrow down which breeders you would like to visit. When in doubt, recede to the reading recommendation and read some more!
The best way to be sure a temperament is what you are looking for is to first learn something about temperaments. The best way to be sure a head style, a size, an eye color, a conformation, or even the sex of a dog is right for you is to learn something about those various factors. And more important than the superficial concepts, are the factors that make your breeder ethical or otherwise (though, I would argue, the sex of your future puppy is not superficial...arguing with myself is often exhausting and pointless. I'm very convincing and very stubborn...)
The best way to know if docking, vaccinating, micro chipping, screening parents for various ailments, and even nutrition are all being done to a standard that you agree with is to - you guessed it - read about these topics and develop your own opinion on them.
Just to recap: go read some stuff. Then meet breeders, exchange emails, and phone calls. In the process develop your own opinions about the topics that matter to you most so you can find a breeder who meets your standards!