Sometimes dog trainers can be terribly unfair to dogs.
The woman who taught me how to train dogs had this mantra: Its never the dog, its always the trainer. What she meant was that if your dog does not do as you ask, the reason is nearly always that you have not communicated clearly what you want or that you are asking the dog to do something that is not possible. You might also be asking the dog to respond to a cue that he hasn't learned yet; we often think that dogs "know" something when they really haven't fully learned and understood what we want.
Maybe your body language tells the dog one thing while your verbal cue tells the dog something completely different. For example, you say, Come here and walk toward your dog: The body language tells the dog to back up or retreat from you, not to approach.