I'd pass on that breeder. They're what I would consider pretty awful.
When I was looking for breeders I referred to the DPCA breeder referral list:
DPCA | Breeder Referral
Be mindful that not all breeders on that list are spectacular, but it's a decent place to start.
I also contacted area/regional kennel clubs and asked for references of good, reputable breeders in my area. This is actually how I found my breeder of choice. A kennel club member was able to recommend her, along with other kennel club members who backed up her recommendation, so I knew I was headed in the right direction. I also contacted reputable training clubs in my region for referrals. People who are involved in and committed to showing and training with their dogs tend to be able to point you toward breeders whose dogs they've met and like. And most people I've met involved in showing and continually training their dogs are looking for good dogs bred to standard. They won't steer you to an unethical breeder whose dogs don't meet standard or can't perform in sports or have poor temperament.
If you're interested in schutzhund, contact a schutzhund club in your area and ask for referrals to Dobe breeders. I'm not involved in bite sports so I'm not much help here, but here's a link to the UDC's website.
UDC They may be able to point you in the direction of some good clubs. (I may be way off on this one though. I don't know since I'm not involved in that sport and the clubs in my area are easily found anyway.)
If you want to focus on AKC conformation showing, contact an AKC kennel club in your area for recommendations. Even if there's not a Dobe breeder in their club, these people go to a lot shows and, since the dog world is a relatively small one, they inevitably know good Dobe breeders around. Here's a link to find one:
AKC Club Search
Really, whatever you decide to go with - Dobe bred for working, show I would recommend you put a lot of focus on health and longevity in the pedigree. A conscientious breeder who does thorough health testing, knows the longevity in the pedigree, and is considerate in pairing their bitch with the right dog (not necessarily the dog they just happen to have) gives your pup the best chance at a healthy life.
Personally, I like to see the following health testing done on the breeding pair:
CERF
OFA or Penn Hip
vWD status
Cardio (annual holters and echoes are a MUST for me)
Thyroid
Liver
I also like breeders that title their dogs in some venue whether it be working or conformation. Ideally, I love when a breeder puts titles on both ends of a dog - conformation and sport. A conformation title will be at the front of the dog's name (CH or Ch) and a sport title will be at the end of the dog's name (CD, RE, MXJ, MACH, OTCH, BH, IPO, etc. are just a few examples - there are
tons of sport titles), hence the phrase "titling both ends". I also prefer a breeder that temperament tests and these certifications will be shown with TT, WAC, ZTP (there may be more of these I've missed).
A lot goes into good breeding and it can be a lot of work to research and find the kind of breeder you're looking for and the right pup, but it's well worth it.