I am sure no authority on the subject but from what I have read it is fairly common for a rescue operation to be understaffed, short on storage space and money and they just do the best that they can.. They might just be able to keep an animal alive and when you adopt one it will require immediate medical care. Some rescue operations may not have those problems at all. If you were obtaining an animal from a rescue operation I think that you would need to check out how they operate and no matter what you see keep the new animal in a separate room from your others for at least a few months.