Tell your friend to go with you to some training clubs .
Ask the handlers which breeders(lines) those that are impressive come from.
CL and any other internet ads will not be the place to find/support good GSD breeders's. They are the places that 'breeder's advertise when they can't find homes for their pups. There are also many facebook pages dedicated to breeder announcements, puppy postings or kennel brags. I see so much traffic on FB it's gotten a bit crazy.