to look for in order to get the best personality match possible
Read both horoscopes, yours and that chosen GSD for compartibility (LOL). This information is for the fools, not for you. You must have noticed that hidden problems with a dog come over time, and if there is something which doesn't suit you - it could be readjusted. All dogs have behavioral problems in that or other way, and that becomes our task to train and retain them. So, you are very welcome to this Forum, and don't hesitate to ask questions about anything your self doubts.
Yes, it is difficult to recognize that or other behavior, and sometimes an agressive strongly self-motivated dog could be easier managed than sad, depressed and seemingly calm dog without knowing his history. There are no untrainable dogs, any dog could be retrained by a kind, patient, non-selfish and heeding to other professionals person. Think about not a possible suitability between you and your future companion, but about training yourself certain things
. For instance: it is recommended not to raise your woice in the first two-three months in order to wait if anything negative pops out itself without stimulation for it to happen. Never at home, never in the street, neither when you are happy, nor when you are angry. Don't say it is easy. But, finally you would benefit from changing your intonations yourself with other people tremendously. There are recommendations to start shaking hands with everyone you know just for the sake of showing your dog a friendly friendly physical contact. Recommendations, recommendations, recommendations on dozens and dozens of things how to build a bridge between you and your dog you are so keen to fall in love with. Please, don't leave it to fate and its chances, tell yourself "I'm successful" and you will be, there is a psychological aspect to any dog training. But... there is always this "but". These cases are very rare, but they happen, I just said that 'there are no untrainable dogs', but 1% of risk from 100 cases does exist. Some dogs were so badly trated from the very start that they become untrainable. It is simply more humane to take your dog to the vet and euthanize him, than throw back into the shelter to his misery. Think about it and prey The Saviour inside yourself.