Here is a favorite article about nerves, temperament, thresholds, and bite-work. A bit long, but well worth the read, and in my opinion, should be required reading for all GSD owners, not to mention breeders!
Elements of Temperament - Scratch My Butt
When I set out to get a GSD for SchH/IPO, I did NOT want a nerve bag, or a reactive low-threshold dog. I wanted a solid, high-threshold dog, friendly and outgoing with people, safe with kids and cats, good out in public, versatile in different activities, a joy to own and train, but also kick-butt serious in the protection field. My choice and preference came from being involved in Schutzhund with my rescue mixed-breed, and training and working with a variety of different GSDs in my SchH club. Some dogs were low-threshold and quick to react and bite, some were serious in the fight, but bidabble and sane and solid, some where all prey-drive with not a serious bone in their body, some were nicely balanced, being successful in trials, and great, all-around pets.
I love to talk about Gryff and people may be getting bored of hearing about him, but he is exactly what I wanted. At club, in seminars, police-dog trainers, world-level competitors love working him - he kicks butt! But he is one of the nicest, most even-tempered, well-rounded dogs that I can take anywhere. High threshold, safe in public, from weirdos in town pretending that they are superheros and air-lazering him as we come around a corner (I just laughed, Gryff cued off my reaction and ignored the person), or little kids running up behind him to pet him (he loves it!). He comes to work with me on most days, has to stay in the car, but breaks and lunch time, we hang out with his work buddies.
Vet is not a problem - shots, examinations, micro-chip implant, he puts up with it with no complaint.
Many others on this forum have bite-trained dog with similar good temperaments and balance as Gryff - in my opinion, this is more the norm than the exception when looking at breeders who understand the true essence of a GSD.