One of my dogs is adopted. A real smart dog. She looks like a pure belgian malinois, but I'm not sure if she's mixed or not.
When we went to get her at the pound, she was tired and sickly looking. Got her home and she won't eat. Turns out she just had worms. Once we got her dewormed she was fine, and eternally grateful. I could tell she had been abused because she was really timid at first, but since she was only about 6 months old at the time, I don't think she was emotionally scarred too badly. She was a breeze to train, is always well behaved, and never causes any mischief. Worst thing she ever does is a delayed reaction to a command. A disapproving tone sets her straight right away.
Later on we got a rottweiler puppy from a breeder. Omfg, she was a training nightmare. Headstrong and completely disobediant. If I was trying to teach her to lie down, then she'll just stand and resist me pushing down on her. If I was trying to teach her to stand up, then she'll lie down and refuse to get up. Getting her to walk on a leash involved repeated training sessions of me literally pulling her across the backyard, with her pulling the other way the entire time. The little bastard growled at me the first day we got her, for trying to take her food. Well, the belgian melinois wouldn't have any of that; she pounced on the rottweiler, had the puppy by the neck, and wouldn't let go! Of course, the puppy was whining in pain, and my dad had to kick the belgian malinois several times until she finally got the wind knocked out of her and let go. The two dogs have gotten along fine ever since.
If I ever get another dog, I would want her at a very young age. I'm not sure if it's environment or the breed, but some dogs just seem to be much more stubborn than others. Make sure you get a well tempered breed.
dfi