"resource guarding vs. protection and throw in fear biting. How can you know the difference IF there IS one?"
We will go piece by piece...I don't care which breed frankly to me it doesn't make a bit of difference with regards to the above.
Resource Guarding~ whatever the dog Truly wants. For example, you gave the dog a bone. Never trained the dog to allow human interaction while it is enjoying it's bone. Human walks up and goes to grab bone, dog bites human.
This is resource guarding, which is very natural for a dog to do.
Human Protection~ Owner and dog walk down the street stranger comes out from the shadows and starts arguing with owner. Dog starts barking and growling at stranger, random person goes to grab dog owners arm. Dog leaps up and bites strangers arm who then releases owner. This dog has successfully protected its owner.
Fear Biting~Dog and owner walk into a store, four people rush the dog to greet it. No one properly introduces themself to the animal going right in to touch the dog. Owner is not paying attention to the dogs distress signals (Dogs eyes and posture) and allows random strangers to surround the dog. The dog tries to pull away but the owner pushes it butt down and tell fido to stay. Random person bends over dog slings arm around the dogs neck to hug it because it's SO cute, Dog bites persons face to get away from the situation. This dog is fearful and not trusting of owners handling or strangers.