Steer clear of sellers who offer puppies well below the usual price range or where the mother isn't present when you visit. Puppy mills refuse to show written vet results or play down the breed-typical risks around the discs and eyes when you talk to them. Another clear warning sign is offers of rare trendy colors such as "merle" (dapple) or dilute colors such as "blue" without strict genetic control: uncontrolled merle pairings carry a high risk of severe eye and hearing damage, up to congenital deafness and microphthalmia, while dilute colors can come with hair loss and skin inflammation (color dilution alopecia). Never buy out of pity, in a parking lot, or without having personally seen where the puppies are raised and the written health records.
On HonestDog, every breeder goes through a sign-up process before their profile goes live: an identity check with ID and selfie, proof of club membership or a §11 permit (the breeding license under Germany's Animal Welfare Act) where applicable, a knowledge test on breeding and animal welfare, and agreement to the HonestDog breeding standards – including no breeding with extreme-breeding traits and no breeding dogs under 18 months. Without a verified §11 permit, a breeder can list at most two breeding females there, and you can flag anything odd on a breeder profile directly via "Report content". When you visit, ask to see the parents' original results. You'll find current litters among the Dachshund puppies on HonestDog.