How to tame this neglected amazon parrot?

Earning back the trust of your bird is going to be a hard process. Although you can't really train it where to leave its droppings, birds have no muscles to control this, you can train it to stop biting. Simply don't pull away. Pulling tells your parrot that it can intimidate you into not touching it. A parrot could easily draw blood, but unless infuriated, most likely will not. Don't, however, touch a bird that doesn't want to be touched, this will make it lose trust in you. If you intend on making inside his/her permanent home, then, yes bring it in the house and let it adjust to the new surroundings for a few days, not touching it, but speaking to him/her often. This parrot is used to being independent, so getting used to being dependent on you will probably not be a welcome experience to him/her. Earning trust will thus be difficult. If he/she doesn't have any, you should place some toys in its cage, but not mirrors, or he/she may bond with their reflection. Repeating the same phrase over and over again will serve as a comfort signal to him/her, and holding treats in your hand will show it that your hand is a source of food, not fear. When your parrot is secure enough with you that it will stand in front of the open cage door in your presence, you can reach your hand in to lift him/her out. Don't make any sudden movements or loud noises around it, especially at first. Don't worry about it only loving you. If you're the only one who interacts with him, he'll bite anyone else :) Good luck!