If an acquaintance wants to take a dog from a shelter, that's fine. Dogs are usually examined by a veterinarian before adoption, and a possible defect, such as deafness, would certainly come to the expert and the shelter staff would draw attention to this fact. However, if someone would like to buy a dog of the breed that bears this risk, I would strongly recommend buying a dog with PP (pedigree), because parents are examined for health before admission to breeding, especially for hereditary diseases, parental couples are selected so as to prevent possible defects and puppies before collection are checked by officials of breeding clubs or veterinarian. A layman usually has no chance of recognizing a hidden defect or deafness in a small puppy. Puppies without a pedigree do not provide these guarantees or medical examinations, on the contrary, they are used in paperless breeding, ie in breeding without any guarantee (ie in "purebred without PP") individuals who have been excluded from purebred breeding for the above reasons. Genetics is a complex matter, I will not go into detail, but it is true that some colors or types of hair (white, merle factor, blue factor, baldness in hairless breeds, etc.) can cause deafness, poor teeth or other defects in connecting unsuitable parent individuals.