I understand where you're coming from, and you clearly have much experience. It strikes me though that it depends on whether you are focusing more on operant conditioning principles or dominance/pack model. I think either could work; the purpose of the back turning as an operant conditioning strategy would be to deprive the dog of the reinforcement it gets from bite-oriented play.
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Sarahaf
One thing is guaranteed. There is no one single answer, book or method. Each dog is different and unique, as are their owners. If there was one method, or book it would have been developed long ago.

Everyone samples from varying techniques and philosophies to derive the system that aids them in achieving their end goal, no matter what it may be.
If you are getting results with the operant conditioning strategy, stick with it. Each person has to find what works best for them. I use that same principle when my dogs commit "lesser offenses". Vizsla's definitely respond to be excluded from their owners good graces. Biting, other than puppy nipping, is just a big deal with me.
If I could clarify my position a bit, it may help.
Bird dog hunters always use the expression "I trained my dog to hunt". Well, this isn't really true. A dog is born with the ability to hunt, and the hunter is actually the limiting factor in their relationship. Simply put, the dog doesn't need the hunter to succeed. A more true statement would be that" I trained my dog to hunt with me".
In order to accomplish this I have to convince my dogs that I have better ideas than they do, and that my way is the most successful way, or that at least we'll have more fun doing it my way. I become the alpha, if you will, in our relationship and the dog doesn't really care that he/she isn't top dog and will adopt a more subordinate position. They're just asking for the relationship to be fair and predictable which is why I always try to establish very black and white boundries for them. I have to assume the alpha role in order for them to accept that we are together, as a team/pack and that we all have our roles.
I was influenced by the writings of authors like George Bird Evans, Havilah Babcock, Delmar Smith, Richard Wolters, and others like them. Their position was always maintained that a person and a dog are a team when hunting. There has to be trust both ways. A bird dog is just under control when in the field. Too much control on the part of the hunter and the dog shuts down and stops hunting. Too little control and the dog is out of control. It's a very fine line that can be influenced by different variables on any given day, but at the core the dog must accept that it is not the alpha on the team. So I guess this is why my position is one of meeting the issue head on. I don't want my dogs to get mixed signals.
The best dogs, in my opinion, are the ones that make you prove it. Not by brute force, or harsh treatment, but by controlling the situation in a manner that is clear. I'll take the dog that says "prove it" over the wallflower any day. I'm not referring to dogs with dominance issues here, but independent, forward minded dogs that are confident in themselves.
Vfloyd
There really is no specific age. It starts very delicately when they are puppies. I'll actually use a rag or something, possibly even just gently wiggle my finger down their tongue to their throat. Their mouths and jaws are just way too delicate at this stage. I'll take the nips rather than risk injury to the puppy.
At 4 1/2 months he's still pretty delicate, even though it doesn't seem so at times, I would go slow. I used to have a thick, soft cotton chew toy. When they would start biting I would put the rope in their mouth to bite on and then not let them spit it out for a few seconds. Make 'em hold it for a bit. Another thing to try is to just gently clamp their nose and mouth shut, sternly tell them no biting, and put them in their crate every time they bite ( when you're sick and tired of having to put him away for the umpteenth time that day, then you know you're being consistent about it). You have to work on it everyday, and everyone in the family has to enforce it.
To be honest though, at 17 weeks he should be **** on wheels. It's the age. Let him grow up, but try to stop/limit the nipping now by having him associate it with an unpleasant after effect, like the stern voice and being put away.
Jenn
It's great that you're achieving results. Biting is a real pain in the rear end, literally and figuratively. There is also nothing wrong with having a short leash n the house. It will put an end to the "catch me if you can game" fairly quickly in the house.
Pay attention to everything the trainer does, and exactly how it's being done. The clearer the picture, the quicker she'll "get it". Ask lots of question so that you are able to reinforce the lessons, and understand the "whys".