This woman claims, that while browsing the dog aisle at Walmart in Lebanon, TN, she was bitten by a german shepherd wearing a "service" animal vest. Unprovoked, she says the dog came up beside her and drew blood when he sank "three or four teeth" into her leg. According to the victim, there was no growling or warning indication before the incident. The owner and dog had disappeared by the time management was alerted, but police were able to identify them thanks to surveillance cameras.
It looks like the victim's main interest is less about personal attention and more about spreading awareness to keep others safe.
This situation was extremely unfortunate and rare. Service dogs are super helpful and trained to save lives. If you should find yourself approached by an unaccompanied service animal, chances are (as you'll see below) the person they're aiding is in need of help.