Abuse or Lack of socialization?

Rescuing a dog is one of the greatest things that a person can do in the animal world. There are so many dogs in need of a home. It can certainly be a challenge obtaining a rescue because we don't know what there previous life was like. A lot of time if a dog is shy, timid or fearful of a particular situation or object they are quickly labeled as having been abused. But is that really the case?
While we are quick to assume the worse, like physical abuse, I feel that lack of socialization plays a bigger hand in how these dogs developed. Dogs have a very small socialization window, the critical period being between ages 3-14 weeks, and most of that time is spent with the breeder. When we acquire the puppy the window shrinks substantially. During the critical period of development you want to expose your puppy to everything and anything that could be a part of their life. Just as quickly as they can form positive associations to people, places, things during this time they can for negative ones too. It is important to keep socialization short and sweet! If you properly socialize a puppy they can adapt quickly to situations or items that may not have been exposed to them in that critical period. They start to generalize that weird objects, people or loud noises are nothing to be afraid off, if exposed in a positive manner.

http://www.pawzforhealth.net/fearful-puppy-behavior/

What about the puppy who doesn't get the proper socialization. Puppy mill dogs are a perfect example.
A puppy who is kept in the barn stall with his other litter mates and never meets anyone except the "breeder" until the day he's purchased it likely to be a very shy, timid puppy. Any object would be new and scary, to be touched or handled would be very invasive. Any quick movements towards the puppy would likely make it back away and cower. A puppy who is cast aside with the mother and pups to live on their own might be more comfortable outside than in a home. These puppies might grow to be 4-5 months or older before they find their first home. While nothing physically abusive happened to these puppies someone might believe they were abused because the way they act.
Socializing a puppy or a dog is such a vital part of owning a dog, if not the most important. It is important for mental stimulation and to continue to build a confident, stable dog. If you have a dog that is older or a puppy that is just beyond the critical period doesn't mean you can't socialize them. It will be a slower process but you can still do it! If you have a dog that you believe to have been abused or maybe now you think they might have been undersocialized you can still teach them and condition them daily to gain confidence. It isn't fair to have dogs go through life fearing weird objects, or particular types of people because we've accepted that is how they are. We need to work to help these dogs and rehabilitate them.
Have you ever rescued or know a dog that is scared of a particular situation or object?