I'm a little late to this, but figured I would share my experience for anyone who might search this thread. I got my first white GSD back in December. Looking back, I should have known there was something a little off (bad genetics maybe, even though I vetted our breeder) when I picked her up since she was the only puppy not to come out of the pen with her mother to greet me. She went through the night in her crate without crying and seemed to adjust well. I even took her home to visit my family for Christmas (there were about 10 people) and she slept on the couch the entire time. She was smart as a whip (learned out to open our dresser drawers the first week we had her- she's still obsessed with socks).
Fast forward a bit. We had her in puppy socialization class at 10 weeks old for four weeks and then moved to the next level class which was also four weeks. She started barking at the instructors for no apparent reason (or so it seemed at the time). Then, she nipped one of the instructors when they tried to give her a treat. We wrote this off since the instructor opened her hand to give our pup the treat and closed it at the last second. After four weeks of that class, we put her in an intermediate level obedience class with the same trainers that was six weeks long. During this time, she became more reactive to people (mainly barking, but some lunging). Using a gentle leader was recommended to us during one class, and when the trainer tried to show us how to put it on, our pup nipped her again (which, after talking to a reputable behavior consultant, was apparently a big mistake on the trainer's part- the trainer should have let us put it on our pup). Anyways, the owner of the training company was brought in to observe our dog during a class because of this, and based on that, thought our dog might be aggressive and recommended a behavior consultant. We met with the consultant at our home for a few hours, and she said in her expert opinion that she didn't think it was aggression, but rather fear/anxiety, and basically chalked it up to GSD being more anxious and neurotic than other breeds, white GSD being even more so, and then having a female on top of that probably made matters worse- however, it looks like we might have some bad genetics as well. She gave us some techniques to try. The first was desensitization, anytime our dog sees a new person she gets a treat before even having the opportunity to react. The second was redirecting her attention (which has been a lifesaver!)- we do so by having a treat in a closed fist down by our side and saying 'front'; the treat is released when she comes to our hand instead of focusing on the 'distraction.' These two techniques used in conjunction with each other have really helped.
I can say, with great pride, our dog has become so much better. She couldn't be taken on a walk without barking and lunging at someone, forget about going to the pet store with us or anywhere with people for that matter. Just yesterday we were taking her to scent discrimination class (which I also attribute to this success by helping her build her confidence) which is held above a church; there were tons of people (20+) in the normally quiet lobby and she walked by without any rewards like it was nothing. We took the summer off from obedience classes, but resumed at the end of August, and her 'usual' trainers couldn't believe the difference. She even let a stranger pet her at the vet! I know there are a lot of mixed views on positive reinforcement and/or desensitization, but I can say in our case it has paid off. Do we still have work to do, of course. But she is leaps and bounds better than what she used to be. Keeping her working has also been a major contributing factor.
So, to recap, in my experience, making sure my dog had stellar obedience, building her confidence through scenting, and desensitization/positive reinforcement really made a huge difference, not only in her life, but also in mine- it can be super stressful having a reactive dog. I expected that GSD were wary of strange people based on all the research I did, but I was not ready for the amount of time, energy, stress, and work I would have to put in. With that said, she is a one of a kind dog, and I really couldn't imagine my life without her antics.