Dachshunds are wonderful dogs but they do have a few traits such as being stubborn, sometimes spiteful and sometimes difficult to housebreak - that can make them a challenge. They also are sometimes known to be bad barkers but with proper training can be taught to behave. They should be able to tell you how they arrived at this conclusion. A reputable breeder will have carefully tested and screened their puppies to determine the personality and aptitude of each one. Hopefully, they have utilized some of the innovative techniques inspired by Dr. Carmen Battaglia.
Puppies learn specific behaviors from their litter mates and mother.
Much of this learning is accomplished at the very critical stage between 6 and 9 weeks. There is no substitute for this interaction. You will be getting a dog whose immune system is better able to handle the world and a puppy who is fully ready to leave his litter mates and transition to a home as an individual. The veterinarian has examined the puppy and declared it to be healthy. You should receive written documentation showing dates, brands and exactly what vaccines were given and what worming preparations were used.