I agree the 'positive' trainers can be some of the most vicious people when dealing with other people than many of the trainers who use 'other' methods with their dogs. Did that make sense? I was on a 'positive only' forum for about a year and have never witnessed such arrogance and rudeness in my life. Yet a local man who runs a shock collar training company is a very nice person, I shudder at the things he considers training a dog but he is nice to people. Go figure, the world is a crazy place.
Just be sure that you can sleep well at the end of your day knowing you have done the best for your dog.
Many methods will work with the majority of dogs, but if you have been unfair to your dog then you need to rethink your methods.
Personally I don't think anyone can guarantee 100% predictability with any dog. Heck, I can't promise that I will perform perfectly 100% of the time.