Did you receive copies of health testing, for both the Sire and Dam?
If the Breeder does not do any health testing (if she is a "back yard breeder"), she most likely wouldn't have any clue as to what sort of maladies are prevalent in her line of breeding. Quite irresponsible yes, but probably not illegal.
At any rate, I really hope Sox gets well soon and you can put this behind you. Do keep us updated!