I'll try to express myself better this time. (longer, but better, I hope) LOL. I seem to not be making my point clear enough. I don't ever think for one minute that the potential isn't there for any carnivore or predator to cause damage to humans. They have big teeth designed to crush bone and tear flesh off bones. They have powerful jaws that exert an incredible amount of pounds of pressure per square inch. Any dog that hasn't had all his teeth pulled can bite. So, there is always potential and it is always prudent to take steps to keep everyone safe.
I think all puppies and adult dogs should be raised in such a way that will tend to prevent problems later on. (idealistic, yes) Some dogs are born with lousy temperaments and while compensation can help, it's not always enough. But preventitive measures should be implimented to give the best chance. That way, the bases get covered. Skipping over vital conditioning type handling raises the odds to one degree or another, of the development of unfavorable issues. So yes, reasonable caution should be in everyone's repertoire when working around animals. I've had horses most of my life and I grew up, keeping that in mind with them too. I hope I didn't imply otherwise.
I would be extremely careful with children with any dog, especially one that had weak nerves. In fact, I probably wouldn't keep a dog that had bitten people because of being startled. I like to see a dog with good, solid nerves and good "bounce back." (being initially startled, but almost instantly over-coming it without freaking out) And that comes from a good, stable temperament and ample socialization before 3 or 4 months of age and continued throughout life. And of course, general good handling.
I merely wanted to clarify that dog to dog aggression and dog to human aggression are two very separate things to a dog. And if a dog displays dog to dog aggression (some types of aggression) they are not necessarily likely to suddenly begin displaying dog to human aggression. I, myself have had a few dog-dog aggressive dogs. (or at least in some cases, reactive) They would have never dreamed of being aggressive to humans...not a "grumpy" or jumpy bone in their bodies.
My Lab was even a little snarky with dogs coming onto the property, even if they set one toe into the property...sometimes even if they were close and we were walking, she'd go after them seriously. But humans...bring 'em on. Full body wag, extremely friendly to all humans. It was a party to her to have anyone come onto her territory. (with one exception where she acted like a real protection dog in the middle of the night when someone was trying to jimmy the door.) I never worried one iota with her where humans were concerned. She adored children and went everywhere with my son and his friends around our private neighborhood. They went fishing together. I never supervised her at all with the kids when they reached around 9 years of age. It never occurred to me back then. Only since the Internet, has the concept entered my head to always supervise children with dogs. LOL.
My last GSD...same thing. He was also wonderful, trustworthy and extremely tolerant with children and strangers coming around and also there was one exception such as the one with the Lab. He really loved having people come over...not your typical, aloof GSD. BUT he was dog aggressive until he got neutered. (he was neutered a little later than puppy hood) He broke his jaw biting into another GSD who ran from him. He was very territorial....against dogs. Never humans.
The kids knew how to behave with dogs and my dogs were always right by their side...best friends. These dogs had the best temperaments of any dog you'd ever see. And they were raised with the kids. That helps. Back then, it never occurred to me to go too much out of my way to condition the dogs to having kids or others take their stuff or handle their food. It just happened. Plus, with the GSD, they were in high chairs and would drop food on the floor. A natural way to convince the dog that little kids are the greatest. LOL. I do remember sitting down with puppies (this was like 30 years ago) and handling their food a little while they ate or giving them something special in their food. I don't remember doing any trading with toys or bones though. They still didn't develop any resource guarding with humans, just with dogs a little bit.
I just finished my last session with a dog that was growling at the owners when they wanted to sit on the couch. This shaggy, rather small Benji-type mutt didn't want to move and they retreated when they didn't have their gloves handy. Yes, you heard me. lol. Gloves. They donned a pair of leather gardening gloves when convenient and would put them on and forcibly remove the dog because you know....they were the "alpha." LOL. He would stiffin up and freeze and show a tooth with a warning snarl and sometimes they'd retreat and sometimes they'd use their gloves. Needless to say, it made the dog worse.
Their other dog was welcome by this snarky beast to get on the couch next to him. He seemed to have a better relationship with the other dog than he had with the humans. So, we worked on some things to get the humans to take control of all the things these dogs (we worked with both) loved or wanted, plus increased exercise and some obedience skills. (all positive reinforcement) And I showed them the on and off game, where the dog learns placement cues and is heavily rewarded for moving over or getting off or going to this other place that is pointed out. The snarky furniture guarding disappeared. I told them to continue to use their placement cues and reinforce and later, they don't have to reinforce every time, but sometimes to keep the dog working hard to comply.
The people also needed to stop speaking so sternly and loudly to the dog. This appeared to put him on the defensive. So they were sending very mixed messages. They'd speak sternly as if they thought they were in control. But then they weren't able to do anything to follow through with what they wanted...sometimes. You usually see, in this kind of situation, owners who are afraid to take charge at all, speak mildly to their dog and give into it every time.
Anyhow, there was a scenario where the dog was snarky to humans in one context and not at all to the other dog. The dog wasn't resource guarding anything else. He had learned that when they take a toy, it is thrown for him to retrieve, which he loved.... so taking things like that was reinforcing. But the couch....no.
Anyhow, you can see where a dog can have issues with humans but not dogs and visa versa. Sometimes both if the human and the dog has given them a reason. But normally, they don't transfer from one to the other. If the human threatens the dog, the dog has a problem with the human. If the dog threatens the dog, he has a problem with dogs. If both threaten the dog, he may wind up with a problem with both. But what causes one doesn't usually cause the other or transfer over to the other.
The Pit bull is a prime example of a dog bred for a certain type of job which makes him tend strongly toward dog aggression. But they have also been artificially selected for a gentle, sweet disposition toward humans. You can take the most dog aggressive Pit bull and not have a worry in your head about him flipping a switch which causes him to suddenly attack a human. Now, of course, there are those who also attack humans. But that's the case with any dog that hasn't been handled properly, socialized correctly or has been mistreated or any number of causes. It is not the fact that he is dog aggressive that he becomes human aggressive. Being dog aggressive, in other words, isn't the catalyst for his becoming human aggressive.
When they start doing that he makes a ton of noise, but can't snap because his mouth is full. So I put one borzoi up and the game is fun for him again, and he'll share his toy with no problem.