He bought from a Schutzhund breeder and probably should have expected the dog to be sharp. I would hope the breeder would take him back.
Of course, you know me, I have a Labrador Retriever, and the only thing she bites is her dinner. She literally loves everyone she meets, she leans on them and gazes up with a big grin on her face and wriggles all over when patted.
What's funny is that, despite that, she's quite protective She will stand between me and anything she thinks looks "funny", and stare fixedly at whatever or whoever she doesn't like. Since she's a dark colored dog (very dark Choc) she probably looks more threatening than a yellow Lab would. She also barks like a ferocious crazy thing at the doorbell or at any stranger outside (until you open the door . .. then she's all over them to kiss them.)