Here's the thing. The reason so many dogs end up in shelters, usually between 1 and 3 years old, is because people do not bother to train their dogs.
You can't train a dog in a vacuum. Sorry, you can train your dog on your own, but that will not make him easy to handle around strange dogs and strange people. Training classes are, in my opinion, a must for dogs that are large and formidable. It is probably a must for all dogs, but owners of GSDs and other breeds that have reputations, have been bred for working, guarding, herding, protection, etc, these dogs need training. They need to be manageable around other dogs and people. Can people do that on their own? Yes, but what is the likelihood that you, stranger, will be able to do it on your own?
If it is my pup, and I have two buyers, and one says they will be taking it to classes, and the other says they train their dogs themselves at home, I am going to sell to the one who is going to take the dog to classes, pretty much every time.
On the other hand, the breeder may be saying this pup will require training because of the lines, the amount of drive the pup has, the temperament of the puppy individually. A novice owner might want to stay away from this puppy. Best to ask the person who knows, the breeder/importer and ask if this is something they require of all purchasers or is it specific to this puppy.