Ours was bad for biting hands too, i got some treats and held one out in a closed hand, if she went to bite i said AT loudly and as soon as she moved away from my hand i gave her the treat, after doing this with her she has calmed down and not as bad, we also use the nothing in life is free and it has worked for us.
it takes time and patience and i don't think these people have either, they could have at least try letting the poor pooch settle in before giving up so easily