The risks primarily lie with you. After receiving the preliminary evaluations by the caretaker of the dog, have a professional evaluate it. Then have the dog examined by a vet (you will be able to do little with a dog that has a traumatic brain injury). With that information you can evaluate your skills and limitations to see if the dog is a good fit.
Even an extremely aggressive dog can be trained to be appropriate in its aggression. While you cannot control the dog 100% you have 80% to 90% influence and even more. Don't let the excuses and myths get to you. You mostly get out of your dog what you put into it-
IF you are WILLING to take the TIME and ENERGY to train it.
Some breeds are strong and large and they know it. It doesn't matter as much how dangerous you may think a particular breed is (e.i. Pit Bull, German Shepherd, Doberman, etc.), what matters more is the individual. If it is big, it is more likely to cause damage from aggression.
Females statistically bite more than males.
Is the dog altered? (Spayed or neutered?)
Some things you can know, others you can't. It is good to know what the past is, but what is faaaaar more important is the now. Too many people get hung up on the past and expect the dog to act as if it was abused, which encourages negative behavior. If you expect the dog to have proper behaviors despite its history, you will have amazing results!
If you aren't willing to invest the time and energy to do what it takes to properly train a dog with an unknown history, you are taking a big risk.