No problem Karen, Please feel free to correct me if I don't interpret your questions as you intend, its hard enough when I am in a training situation to sought out a problem, and then I have the dog to tell me whats going on!
Blogs and books always have there limitations to training as its easy to read into something that isn't there or mis-diagnose the problem in the first place.
Training the back command is a task in itself, and needs to be done in isolation from other ( directional) commands in the early days. I introduce the back command when the dog is happy with the straight forward `On and fetch' command with seen retrieves. i.e. the dog is steady to throw and fall of dummy, and retrieves on command. Then whilst the dog is sitting I'll stand in front and throw the dummy over the dog to land behind them. Often the dog will move to face the dummy, but you must resit the dog to face away if this happens before giving the `back and fetch' command ( with the hand signal). Once this begins to click I will introduce the memory seek back over increasing distances of retrieve and increasing distances from the dog. The dog has both its memory of where you dropped the retrieve and your foot trail to guide it, so this really builds confidence quickly and allows the back command to become established.
Remember don't be in too much of a rush, there are plenty of variety and ground to re cover to keep the dog from getting `bored', rather than steaming on with more and more new commands, as the danger is you'll inadvertently start treating and rewarding the basics less than you should and the dog will do likewise and start taking liberties.
Hpr trainers are few and far between, it was good that the trainer you approached admitted his lack of experience, as more often than not they don't, and these dogs need a different approach and understanding. Their working traits are unique to their group and not an amalgamation of their functions. If you can join a hpr training group they are extremely helpful and welcoming, the GSP Club run several all over the country and they usually meet once a month, some on weekends some in evenings. They will often have a `trainer' but its more about pooling knowledge and helping each other out, attending GWT's will also be of great value as you may pick up contacts closer to you in the form of `training buddies', they may be different breeds but remember as a group we are all in the same boat when it comes to help getting our dogs trained!
Peter