Yup, I've seen abused dogs.....and I've got abused dogs living with me.
Colby was most likely abused.....I think she was put in a sack and thrown out the window of a car.....and the shelter found her (don't remember exactly what the shelter told us happened to her). I consider throwing a dog abuse.
When we got May she terrified, a bag of bones, and still had milk (had obviously been used for breeding). Whenever my dad went to walk her she'd slip her collar and run all the way home. She was terrified of almost everything. Now she can walk past huge roaring trucks with no problem, she likes my dad....she doesn't like thunder or yelling though.
Tippy was abused and neglected by our druggie neighbors. They two other dogs, Mr. B and Nanook, and Tippy whom they got from a farm, and they let them roam. Their garage was full of garbage, later we found out they had rats, the dogs had to live under their deck, and as far as I know they didn't get much food (the six-year-old boy living there said he fed them, but it didn't look like Tippy got much at all). After we fed and pet her Tippy decided to come to our house and never leave. The neighbors let us have her.
I also know someone who chains their lab to a dog house outside...he looks fed, but when I met him, he was desperate for attention and covered in poop.