thats not true in general: it depends heavily on the breed, the region, and the breeding association and/or breeder. In any case, you should always do your research before buying a puppy. Purebred dogs typically come with a pedigree certificate, which includes information about the inbreeding coefficient and hereditary diseases in the family line.

please dont buy from mass breeders, dont support “cruelty” breeds. if a breeder sells you a puppy right on the spot go away. Serious breeders carefully select the families for their puppies and usually want to get to know you over multiple visits.