The simple fact that your pup was a mere 6 weeks old is a case in many states for a law suit, but I would guess that in your own state, they haven't legislated that pups should be a minimum of 8 weeks...check into that, though.
I work at Petco. I see so many cases of pups coming in from the nearby Petland who are severely underweight, whose owners report that the pups had kennel cough, had Parvo, had other diseases. I simply can't believe it.
What I wish is for these people to get together and file a Class Action suit against Petland, or whatever the pet store where you got your pup from, and stop these completely heartless people from ever again having a living animal in their facility.
The only thing I can compare the abuse of helplesss animals is this: When you go to any other store, they present their 'product' to its best advantage. If you entered say a Wal Mart store and they had their clothes laying on the floor, had broken boxes of housewares...would you even consider buying the product??? Of course not. But people by damaged pups every day from pet stores.
It isn't that Petland, etc., can't properly care for their animals. They, IMO, think that if the pups appear near death, people will be more willing to buy them to 'save the life' of the pup.
In fact, the buyers only sentence the parents of said pup to producing yet another litter. The parents who live in hell on earth.
And the buyers, as you have discovered, get little recourse when they try to recoup anything from the damaged 'product' they purchased.
These pet stores who sell pups/kittens HAVE to be stopped.
Finally, I have to say that threatening to report people for stating the obvious is really idiotic on your part.