As a dog Behaviorist I see a lot dogs. The new dog owners with the puppies who reach out are the smartest. They call and get advice and future training. Those owners and dogs have the best chance for keeping that puppy.
It is easier to mold then to fix. Some come born with temperament issues. If left alone those traits grow stronger.
Ex/ Shyness, noise sensitive, fear. Many times if not managed they come to the bite stage.
If your new puppy or adult dog is showing behaviors you do not like you need to change them or resolve to live with them. I like to change them.
Your cute puppy lunges to visit the neighbors dog. When you can not stop this another behavior appears. The pup gets frustrated and shows another frustrated trait. Barking is one. Now lunges and barks. If this behavior is stopped here as a puppy it does not grow. If not it does until it looks like a raving mad dog trying to kill another. Very scary but also embarrassing to the owner of the crazy looking dog. If this was stopped at the lunging at other dogs stage the rest would never show up. Since it has shown up it can be eliminated. It can.
The older the dog and the longer the dog has done the bad behavior the longer it will take to go away.
When it does grow . Dog lunges, barks, shows teeth. Finally we as humans accept that because we just do not know what to do. I can but most can not. So yes they need a dog trainer at this point because you have
Harsh I know but those are the choices I hear with the dogs I meet and train.
Happy Dog Training